The City Hall killer was an HIV-positive man who made meticulous preparations for his own death before setting out to assassinate a political rival who he believed was blackmailing him because he was gay, law-enforcement sources said yesterday.
Before meeting up with his murder target – Brooklyn Councilman James Davis – Othniel Boaz Askew, 31, laid out on a living-room table his last will and testament, along with a detailed note to a brother specifying where all his bank accounts and other valuables were, police said.

Cops also found his HIV medications elsewhere in his fastidiously neat Fort Greene apartment.

No suicide note was discovered, but cops searching for a motive said they were looking through the contents of Askew’s laptop.

Police sorted through evidence and witness testimonies yesterday and said the ambitious Askew was despondent over inability to get on the primary ballot against Davis. He also was enraged by his belief that Davis was doing everything possible to squeeze him out of the race.

“He just flipped out over the political rivalry,” said one investigator. “He couldn’t handle not running. It looked like he wanted to go out in a blaze of glory . . . and what bigger stage than City Hall?”

Law-enforcement sources said that hours before he gunned down Davis, Askew told the FBI the councilman had offered him $45,000 to give up a primary election challenge and threatened to hurt his family if he did not.

Askew also claimed Davis offered him an additional $15,000 annually and a no-show staff job. A City Council spokeswoman denied the allegations, and investigators said they had not corroborated Askew’s claims.

But a well-placed source told The Post Davis had done a thorough background search on Askew, found records showing he had been involved in a gay domestic dispute in 1996, then used the information to blackmail Askew into withdrawing from the race.

The night before the killing, Askew had been hanging out at Charter-revision forum at the Brooklyn Public Library, where he was caught on tape by a local TV crew.

Police found a stack of political posters and flyers from past Davis campaigns in Askew’s apartment.

While no independent toxicological studies have been released, police said they believe Askew was HIV positive. They said they found prescriptions for Paxil, Zarret and Viagra, as well as gay porn and sadomasochistic material.

Investigators said Askew bought a silver 40-caliber gun with a seven-shot clip in North Carolina in May 2001, and that Askew wore the gun in his waistband on Thursday. He had seven additional bullets hidden in his left sock, and cops speculated he had planned first to empty his gun on his opponent, then to painstakingly reload it.

All seven rounds were fired and every one hit Davis – two of them ripping through his body and out exit wounds.

A card found in Askew’s pocket read “I am not a donor. I’m Jewish,” they added.

Cops also found a bottle of Valium pills.

Investigators said that hours before City Hall erupted in gunfire, Askew and Davis argued at a Brooklyn barbershop, then drove to Manhattan with a Davis aide. It was unclear whether Askew planned to go into City Hall, or how he planned to evade metal detectors.

Court records show that had a history of domestic violence: the then-24 year-old Askew was arrested on Dec. 29, 1996 and charged with felony assault on charges that he beat his boyfriend with a hammer inside their West 43rd Street apartment. Mario Romero told cops that Askew “repeately struck (him) over his head, face and body with a hammer.”

According to the criminal complaint, Romero had head wounds and lacerations over his body. Askew was never indicted and was allowed to plead guilty to second-degree harassment after promising to keep his nose clean for a year.

Askew was also arrested in Manhattan in 1999 under the name “Neal Askew” and charged with petit larceny after stealing a bag filled with about $900 worth of property, including jewelry and a cellphone, from a friend. The case was knocked down to a violation.

In addition, Askew was at the center of at least two nuisance suits: he unsuccessfully sued a ski lodge after a skiing accident in the 1990s, then sued a Fire Island gym for $1 millon in 1999, saying he had been injured doing bench presses. The case was thrown out after Askew refused to take a court-ordered physical exam.

Askew claimed to be an Orthodox Jew, a Yale Law School graduate, a Gulf War veteran, a real-estate developer, and a future senator.

Yale could not immediately confirm the claim, officials confirmed Askew had served in the Air Force, and there was no record of any real-estate development experience beyond work on his Brooklyn home. Neighbors in Long Island said he had been brought up as a Jehovah’s Witness.

Described as a fast-talking charmer, the dapper Askew used several names, and had a reputation as an eccentric with an unlimited imagination. He also had a piercing gaze and a sometimes disturbing manner.

“He was slick,” said neighbor Larry Caparaso, who lived near Askew on a street lined with million-dollar brownstones. “He could have been a con man. A professional con man.”

Residents in Fort Greene said they had often seen him surrounded by mostly young, white supporters as he glad-handed locals dressed in a suit and wearing close-cropped hair.

“He was a little too friendly,” said neighbor Dennis Canning. “He seemed nice, but there was something about his demeanor that made you a little uneasy. He was always assessing you, like he wanted to see into your soul. And I don’t want anyone seeing into my soul.”

Askew’s father told the Post his son was born in Park Slope, schooled in Brooklyn and Babylon, L.I., and studied accounting at C.W. Post College. He worked for Roche in New Jersey and served in the Gulf War.

One neighbor in West Babylon, L.I., who did not want to be identified, described the young Othniel as “a very nice boy, very considerate.

“He was the kind of person who shoveled snow for you,” the neighbor said.