Another domino fell Thursday in the ongoing investigation of a north shore drug task force when Rose Graham pleaded guilty to three counts of conspiracy to distribute cocaine and marijuana in a St. Tammany Parish courtroom.

Graham, who is not a law enforcement officer, admitted in court to conspiring to sell the drugs at the behest of two Tangipahoa Parish Sheriff’s Office deputies who were members of a U.S. Drug Enforcement Administration task force.

Her sentencing was delayed until Oct. 13.

Graham stood with her lawyer, Robbie Rees, during the brief hearing, assuring 22nd Judicial District Court Judge Reginald Badeaux that she understood the severity of the three felony counts and the possibility that she could serve prison time.

But at points, she also appeared frustrated that she was in court at all.

“I was doing this for the police. Why am I in trouble?” she said to Badeaux.

“That sounds like a defense,” Badeaux replied, adding that he needed to be sure she wasn’t being coerced into pleading guilty.

Graham told him she was not.

As a condition of her plea, Graham must cooperate with all state and federal law enforcement agencies investigating the matter. In return, the state agreed not to prosecute her for any other drug crimes.

In court documents attached to her plea agreement, Graham admitted going to the parking lot of a Madisonville-area restaurant to sell 5.3 pounds of marijuana for $1,750. The buyer was an undercover trooper who discussed purchasing other drugs with Graham, including another 10 pounds of marijuana.

Graham was also supposed to sell cocaine given to her by then-Tangipahoa Parish Sheriff’s Deputy Johnny Domingue, a member of the DEA task force. Domingue is accused of having received the drugs from another Tangipahoa deputy, Karl Newman, another member of the same task force.

Newman had signed some of the drugs out of DEA evidence stores and given them to Domingue, prosecutors allege.

Both Domingue and Newman have been charged. Domingue pleaded guilty last month in a St. Tammany court. Like Graham, his sentencing was delayed for six months, pending his cooperation with authorities.

Newman has charges pending in St. Tammany and Tangipahoa parishes.

The investigation seems to be focused on DEA Special Agent Chad Scott, also a former Tangipahoa deputy, who has led a DEA task force on the north shore for several years.

While the investigation into Graham, Domingue and Newman has been led by the Louisiana State Police, sources said federal authorities have taken over the investigation into Scott, who has been both praised as a model agent and criticized for using improper methods.

Follow Faimon A. Roberts III on Twitter, @faimon.