Authorities attempt on a daily basis to glean intelligence from jailhouse communications, monitoring inmates’ telephone calls and screening their mail.

The eavesdropping can be a mundane task. But in one recent case, watchful eyes at the Orleans Parish Sheriff’s Office may have saved the life of a witness in an already shocking murder case.

Over the summer, deputies intercepted a suspicious letter penned under a fictitious name and inmate number. The correspondence was addressed to a local tattoo artist whose older brother, Thayon Sansom, is in the Orleans Parish jail awaiting trial on kidnapping and murder charges in the gruesome slaying of Lindsay Nichols, a 31-year-old mother.

The letter, described by police as part of a murder-for-hire plot, ordered its intended recipient to “have a known witness executed,” according to court documents, and contained “instructions on how and where to find the known witness.”

Detective Robert Barrere, of the New Orleans Police Department, added that he “strongly believed” Sansom to be the author of the letter, noting that it contained at least one reference to “my dear brother” and was addressed to Sansom’s brother’s tattoo shop, We Bleed Ink, on Washington Avenue.

In a telephone interview last week, Sansom’s brother, Trevone, sought to distance himself from his brother and denied any involvement in a scheme to bump off a witness. He said he has cooperated with the authorities, even as they searched his business for additional letters he received from the jail.

“As of right now, I know my brother is in desperate times,” Trevone Sansom said, “and he’s doing all kind of stuff I honestly wouldn’t have thought he would be doing.”

Police have accused Thayon Sansom, 30, of fatally shooting Nichols in New Orleans East on June 21, stuffing her corpse in the trunk of her car and then setting the vehicle on fire on a deserted stretch of roadway near Interstate 510. He faces an automatic life sentence if convicted as charged.

As the authorities continued to investigate whether Thayon Sansom received any assistance during or after the killing, court records show police became concerned in recent months that he might be trying to eliminate evidence — including a witness — from behind bars.

Following up on the letter, Barrere listened to jailhouse phone calls between the Sansom brothers in which they spoke of the intercepted letter, “as well as an additional letter that Trevone Sansom had already received at his tattoo shop,” according to court documents. The detective, in applying for a search warrant, asserted that he “strongly believes that the additional letter may (contain) additional instructions on how and when to kill” the witness.

A Sheriff’s Office spokesman did not respond to a request for comment on the intercepted letter.

However, a person familiar with the investigation said the office had been keeping a close eye on mail sent to Thayon Sansom’s tier as part of an unrelated contraband investigation. He referred to the discovery of the letter as “divine intervention.”

Exactly what investigators seized from the tattoo shop is not clear, though Trevone Sansom said authorities took other letters his brother had mailed to him. Tyler Gamble, an NOPD spokesman, declined to comment on the search, citing the ongoing investigation. He said no one other than Thayon Sansom has been charged in Nichols’ death.

Keith Sanchez, an attorney for Thayon Sansom, declined to comment Monday, but he noted that his client has not been hit with any new charges in connection with the intercepted letter.

Court documents make clear, however, that detectives have investigated the possibility that someone else was present when Nichols was killed.

According to police, Thayon Sansom met Nichols at a nightclub on Downman Road the night of the slaying. Nichols, a bookkeeper for a Texas construction company who was in town visiting family, got Thayon Sansom’s phone number before leaving the club about 4 a.m.

A few minutes later, cellphone records show, she phoned him twice before calling 911 and telling a dispatcher that an irate man she’d met only once was standing outside her car aiming a gun at her. The man’s voice became increasingly audible as the call continued, and he accused Nichols of giving his address to someone else. At one point, Nichols could be heard screaming as the man in the background demanded she open her mouth so he could shove a gun inside it.

Nichols’ body, bullet-riddled and burned, was found several hours later in the charred trunk of her vehicle after firefighters extinguished the car fire at Lake Forest and Michoud boulevards. Witnesses later told investigators that Thayon Sansom had been seen standing over the open trunk of Nichols’ car at that location.

Sansom told authorities that he had met Nichols at the club and spoken with her. But he denied involvement in her killing, saying he had gone home to his apartment after leaving the establishment.

Investigators searched through Trevone Sansom’s cellphone records and learned he had received a call from his brother “on the date and time of the homicide.” The brothers exchanged “several additional calls,” according to court filings, and “cell site information placed Trevone Sansom near his brother’s apartment and near the location where the decedent’s vehicle was located around the time of the homicide.”

“It’s just a bunch of mayhem going on, and I’m trying to keep myself clear of all of this because I have a whole lot at stake,” Trevone Sansom said last week. “I’m not even trying to get crossed up into my brother’s mess.”

Nichols’ mother, Jolene Dufrene, of Des Allemands, said she has long suspected that others were involved in committing or covering up her daughter’s killing.

“I’m sure he had accomplices to go bring her body down the road,” Dufrene said. “There’s got to be somebody else. That’s just my feeling. I don’t think he just drove over there and walked away.”

Follow Jim Mustian on Twitter, @JimMustian.