By Tracey Kaplan

SAN JOSE — Ending weeks of speculation, Santa Clara County prosecutors said Thursday that 49ers star linebacker Ahmad Brooks will not face any criminal charges for bonking a teammate in the head with a beer bottle.

Two eyewitnesses and the teammate, Lamar Divens, had told San Jose police in early June that Brooks struck Divens on the head with a Heineken bottle three times, leaving him bloodied and requiring three stitches. At the time of the June 8 incident, Divens said he wanted to press charges, but he changed his mind a few days later, according to police reports.

Assistant District Attorney Karyn Sinunu-Towery said Brooks has a viable self-defense claim for why he repeatedly hit Divens — because Divens, who is 64 pounds heavier, had shoved him at a party about a month before, causing him to fall down and cut his leg slightly.

“Brooks believed Divens was going to knock him to the ground, as he had done a few weeks earlier,” according to a four-page memo Sinunu-Towery released Thursday. Brooks was first interviewed by DA investigators July 15, five weeks after the incident, not by San Jose police who conducted the initial “cursory” investigation, according to Sinunu-Towery’s report. She said police did not follow up because Divens minimized his injuries and said he didn’t want to press charges.

The memo cited four other reasons for the decision: Divens has flip-flopped on cooperating with the prosecution; he initially characterized his injury as nothing but blood; he made statements about the altercation that can’t be corroborated; and it is arguable he is using the criminal justice system for financial gain because he asked Brooks for $1 million.

However, Sinunu-Towery said in her memo, while “I do not condone the behavior of Brooks,” an assault charge cannot be proven beyond a reasonable doubt to 12 jurors.

The decision is likely to please fans. But it may do little to quell the widespread perception that top athletes with multimillion-dollar salaries, legions of fans and ties to popular sports franchises either get off easy compared to the general public, or benefit from more cautious, thorough investigations than ordinary people do before prosecutors seek a felony warrant for their arrest.

The case took an unusually circuitous route through the DA’s Office, winding up where it started — with a decision not to file assault charges. Initially, the group of prosecutors who issue cases decided it was a “no-file” because of insufficient evidence. But a high-ranking lawyer thought it bore a second look and brought the case to Sinunu-Towery for review since she supervises the team that handles assaults.

Line prosecutors then obtained a felony assault warrant from a judge for Brooks’ arrest — only to see it frozen a few days later by higher-ups, who wanted the matter investigated further. Speculation centered on whether the office would file a misdemeanor punishable by up to a year in jail, a felony punishable by a maximum of four years behind bars or not file at all.

The star linebacker signed a six-year contract extension last year worth $44.5 million, with $17.5 million guaranteed. Last season, he helped clinch the NFC Championship.

The controversy stems from an incident in which Brooks, 29, allegedly struck 49ers nose tackle Divens three times in the head with a beer bottle and then punched him in the face during an argument over car keys outside Brooks’ house in San Jose. According to police reports, Brooks, who was drunk, demanded his car keys back from Divens, the designated driver. Divens was reluctant to give Brooks the keys, which prompted the unexpected attack, according to court documents.

But Sinunu-Towery said Brooks told the office’s investigators that he wanted the keys back to get into his house, not to drive his car.

According to the initial police investigation, Divens said Brooks then allegedly threatened Divens, saying if Divens didn’t leave, he would get his gun. But no one else heard Brooks say anything about a gun, both the police and DA’s investigations found.

Prosecutors weigh dozens of factors in filing any case, including their chances of winning and whether filing is the right thing to do.

Winning a felony assault case against an athlete or coach can be difficult — even when the victim’s injuries are significant.

Earlier this summer in San Luis Obispo, a jury acquitted former Oakland Raiders and Cal Poly assistant football coach Randy Hanson of felony assault with a deadly weapon, even though he broke the victim’s nose and gave him a concussion with a beer bottle.

That spared Hanson a possibly lengthy prison sentence. However, the jury did convict Hanson of felony battery and misdemeanor assault, and he was sentenced to 120 days in jail.

Contact Tracey Kaplan at 408-278-3482. Twitter.com/tkaplanreport.