Alex Williams picked up his first drug conviction at age 13. Wednesday, he finished up with the only honest job he’s had in the nearly 30 years since.

Williams made some $93,000 as a paid informant for the FBI, helping build the sprawling racketeering case against members of the Black Souls by feeding police and federal agents information about a street gang that prosecutors say was behind multiple murders and controlled a thriving drug market on Chicago’s West Side.

He spent five days on the witness stand, recounting for jurors his years hanging out almost daily with the six alleged high-ranking Souls seated across the courtroom from him, including his former Cook County Jail cellmate and purported Souls kingpin Cornel Dawson.

The last three days, he was badgered by defense lawyers, who were more focused on the illicit side jobs he undertook while on the government payroll — the four times his FBI handlers caught him selling drugs, and his arrest for drug dealing just last month in the Downstate town where he’d been relocated at government expense.

As his FBI handler testified last week before Williams took the stand, informants seldom are Boy Scouts.

“To get the access they have, they’ve committed crimes,” he said.

Williams is a key witness, having testified he helped investigators record dozens of conversations with top Souls members over nearly two years, then helping translate the jargon when they transcribed the tapes. Leveraging his jailhouse friendship with Dawson, Williams testified he spent “almost every day” hanging with top members of the Souls and selling drugs on their turf — even though Williams himself was a member of a rival gang.

Williams also testified that in October 2012, he drove past the scene where Souls member Duavon Spears shot and killed police informant Claude Snulligan, and later helped police identify Souls members on surveillance video that showed them milling around a nearby parking lot near the time of the shooting.

Williams testified he called called Chicago Police Officer Michael Lipsey from the scene of the shooting, then called Dawson.

“(Dawson) just told me, ‘it was a good day in the ‘hood,’” when he learned Snulligan’s body lay in the street near a Souls’ hangout, Williams said.

On top of cash for rent, expenses and his relocation Downstate, Assistant Public Defender Kathryn Lisco said prosecutors also helped Williams get a sweetheart deal after separate arrests for both selling drugs and assaulting a police officer Downstate after the government had paid to move him out of Chicago. Williams had faced up to 60 years in prison but pleaded guilty last month to reduced charges and is line for a three-year sentence, Lisco said.

“So, when this deal is done for you, you might only be looking at a year and a half (of actual jail time)?” Lisco asked him.

Prosecutors already have put a handful of former Souls on the stand, and more are expected to be called as witnesses during the course of the trial, the first case taken to trial under state racketeering laws adopted in 2012. The case is set to last into December.