Authorities said Thursday that they continue to pursue other people in connection with the February killing of Reserve couple Lakeitha and Kenneth Joseph, even as they announced the arrests of a 25-year-old woman and a 37-year-old ex-con on suspicion of murder in a double killing that ended with a seemingly well-planned body dump into the Intracoastal Waterway in New Orleans East.

Police said arrest warrants for Brittany Martin and Horatio Johnson were issued Tuesday, and they turned themselves in the following day. Both were being held in St. John the Baptist Parish but are expected to be moved Friday to Orleans Parish and booked with two counts each of second-degree murder, NOPD Superintendent Ronal Serpas said.

According to state corrections officials, Johnson was released from prison in August 2011 after serving about half of a 35-year sentence on a manslaughter conviction in St. John the Baptist Parish, where he admitted gunning down a man who was found in a Reserve schoolyard two decades ago.

Serpas declined to name any additional suspects in the case, describe a motive or shed much new light on the investigation. But speaking at a news conference Thursday with St. John the Baptist Parish Sheriff Mike Tregre and state and federal investigators, he warned others who may have been involved or know about the crimes to step forward.

“I would strongly recommend that we know more than you think,” Serpas said. “We know, and it’s time for you to come forward.”

He acknowledged that blood found in a 2010 Dodge Caravan that Kenneth Joseph had borrowed from his sister on Feb. 18 tested positive for a mixture of the two victims’ blood. Police later recovered the van in an apartment complex in College Park, Georgia.

But Serpas refused to answer questions about any crimes that may have been committed before the couple were dumped. And he declined to say whether detectives believe the Josephs, bound by rope and weighted down, were living or dead when they landed in the water. The Orleans Parish Coroner’s Office has classified the deaths as drownings, saying autopsies showed they were alive at the time.

The couple’s bodies were found separately in the water, tied with blue nylon rope, weeks after they were last seen Feb. 18.

Fishermen spotted Kenneth Joseph’s corpse March 22, tethered to the handle of a 30-pound kettlebell, nearly two weeks after his wife’s body had turned up. Detectives said the kettlebell was used in “an attempt to weigh Joseph’s remains down under the surface of the water.”

In a search warrant, a detective described tracking down a purchase by Brittany Martin, who used a credit card at a Kenner Wal-Mart on Feb. 19 to buy two kettlebells, two fleece-hooded sweatshirts, three pairs of “gripping gloves,” fishing line, blue utility rope, two pairs of shoes and a bottle of degreaser.

Serpas credited video surveillance from the store where Martin allegedly purchased “the murder weapon” as key to solving the case.

Serpas said Johnson and Martin delivered the van to another known person “to be destroyed.” That seemed to contradict an initial story that Frank Mike Jr., another man arrested in the case, allegedly told investigators, saying he found the Caravan in the driveway of a home he had been renovating on Beechwood Court in New Orleans.

Mike is accused of taking the Caravan to Georgia after the murders, attempting to wipe it free of fingerprints and abandoning it. Detectives tracked down a surveillance video from a Travelodge hotel in Georgia, showing Mike driving into the hotel, where he checked in on Feb. 21, according to an affidavit from FBI Special Agent Timothy Denny.

A federal grand jury on April 25 indicted Mike for knowingly transporting a stolen vehicle across state lines. He pleaded not guilty this week.

Mike called State Police on April 3 and told detectives he’d found the van at his home, then gotten a call from a friend who said “we pulled off a little move in it.” According to the affidavit, Mike said he asked the friend if he could take the van to Georgia to go clothes shopping, then got rid of the car in Atlanta after seeing news reports indicating it was “possibly related to a stolen van which involved two missing people.”

He admitted that he “observed blood in the van,” Denny stated.

Tregre lauded investigators who made repeated trips to Atlanta to pursue the investigation, although Serpas declined to say whether their focus in Georgia went beyond questions about the van.

Court records from Johnson’s 1994 case show that he was originally charged with second-degree murder for the killing of Keith Selders, who died of a gunshot wound to the head. His body was found in a schoolyard in St. John the Baptist Parish.

Johnson gave four taped statements, including a confession that he shot Selders, a court account shows. He testified at his trial that Selders came to his home asking to buy crack cocaine but then pulled a gun on Johnson, stole his crack and ran. Johnson told the jury he went after Selders with a shotgun, shot him and tossed the weapon into nearby bushes. He claimed Selders had threatened his life, arguing that the killing was justified.

The jury didn’t buy it.

Laura Selders said her son was 30 when he was found shot in the face on Nov. 12, 1993, on the grounds of Fifth Ward Elementary School in Reserve. A cap covered the wound. The embalmer used mud to re-create half his face for an open-casket funeral, she said.

Selders said her son and Johnson, who was 17 at the time, hung out together with about a dozen others.

“My son always acted like a big brother over them, a whole lot of them hanging together like a gang. It bothered me then. He was always in my house. How could he do something like that?” she said.

“I heard my son was on his knees, begging him, ‘Please, don’t shoot me,’ and (Johnson) looked at him grinning like a Cheshire cat, saying, ‘Oh, you’re going to die.’ ”

She said she didn’t understand why Johnson served just 17 years of his sentence before being released.

“For me, he’s a cruel person, so whatever he gets, he deserves it,” she said. “You can’t just go around killing people.”

Johnson appealed his sentence, claiming the 35 years was “excessive for a first-time offender,” court records show. He also claimed the jury improperly relied on his confession, which he repudiated.

An appeals court rejected the appeal in 1995 and turned him away again in 1999. With “good time” credit, he was released in August 2011 and is currently on parole supervision, according to the state Department of Corrections.

Serpas declined to say whether the others being sought may have been involved in the murders. A report cited authorities saying Johnson, of LaPlace, was a business associate of Kenneth Joseph. Serpas declined to confirm that or describe any connection or suspected motive.

Serpas and Tregre touted an aggressive investigation that included the FBI, U.S. Secret Service, the federal Drug Enforcement Administration, Harbor Police, State Police and the St. Bernard Parish Sheriff’s Office.

“The criminals do not care where the parish line starts and stops,” Tregre said.

“Piggy and Ken Ken, the little couple from Reserve who left their home and never came back again,” deserve justice, Tregre said, and “the people who did this need to be in jail for the rest of their lives.”

Follow John Simerman on Twitter @johnsimerman.