San Francisco 49ers defensive lineman Ray McDonald will not face domestic violence charges in connection with a dispute at his San Jose home with his pregnant fiancée because prosecutors cannot prove a crime occurred, the Santa Clara County District Attorney’s Office said Monday.

San Jose police had arrested and jailed McDonald on suspicion of felony domestic violence after responding to his home on Bentley Ridge Drive early Aug. 31, after a 30th birthday party that McDonald had thrown for himself. Investigators said his fiancée had “visible injuries.”

But after a lengthy review, the office of District Attorney Jeff Rosen declined to file charges.

“We have determined there is insufficient evidence to file charges against Ray McDonald,” said Deputy District Attorney Lindsay Walsh. “Both parties agreed that Jane Doe (McDonald’s fiancée) struck Ray McDonald first, and her minor injuries are consistent with restraint rather than an attack. Due to conflicting accounts, the lack of eyewitnesses and the lack of cooperation on Jane Doe’s part, we cannot prove that a crime occurred.”

The case garnered national attention in the wake of arrests of other NFL players for alleged domestic violence.

McDonald has suggested he was wrongly arrested. “The truth will come out,” he told reporters after being released on $25,000 bail following his arrest. “Everybody knows the kind of person that I am. I’m a goodhearted person.”

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On Monday, McDonald said in a statement released by the 49ers, “I appreciate the seriousness of the situation and I understand and respect that law enforcement had a job to do, which is why I cooperated fully with their investigation from beginning to end. I am relieved that the DA's office has rightfully decided not to file charges. I want to thank everyone who was supportive during this difficult time.”

According to the district attorney’s office, McDonald’s fiancée, who was ten weeks pregnant, struck him at about 2:30 a.m. during an argument, prompting him to “physically restrain her.”

“The two scuffled,” prosecutors said. “McDonald then forcibly attempted to remove her from the home.”

A memorandum on the case released by the district attorney’s office describes a squabble that turned physical, and began earlier in the night after McDonald grew concerned about text messages he was receiving from women he had met the night before his birthday party.

McDonald called the 49ers’ security director, who in turn called Sgt. Sean Pritchard, a San Jose police officer who did private security for the team in his off hours.

Pritchard went to the house two times that evening to see McDonald, who believed one of the women who had sent text messages might be at the birthday party because she was describing what McDonald was wearing, the district attorney’s office said.

Guests at the party were apparently unaware of the drama as they began to trickle out. One visitor, however, stopped by a room where McDonald’s fiancée was sleeping to warn her about women “getting too friendly with McDonald,” prosecutors said.

They said McDonald’s fiancée then got dressed and confronted a woman talking to McDonald, asking her to step outside. McDonald told investigators he was embarrassed and upset by this action, and concerned about his fiancée’s safety because she was being aggressive and was pregnant.

The fiancée said she and McDonald argued, and that he “indicated that she was an unfit mother and threatened to take her baby.” Both parties told the district attorney’s office that McDonald’s fiancée struck first — though she said it was a single push, while he recounted multiple blows with a closed fist.

McDonald “forcibly attempted to remove her from the home,” at one point grabbing her neck while she was fighting back, which resulted in a “visible injury,” prosecutors said. They said his fiancée broke free and ran upstairs around 2:39 a.m., at which time McDonald called Pritchard a third time and said, “I need to get this female out of my house.”

Two minutes later, officials said, McDonald’s fiancée called 911.

“Hello. I’d like to press for a domestic violence,” she said, according to a partial transcript of the 911 call released by the district attorney’s office. “My fiancée, he’s trying to pull me out of the house. He’s drunk. I think he’s calling the cops. he’s trying to get me out.”

Responding police officers, who arrived after Pritchard, said McDonald was calm and cooperative, and that his fiancée — who was visibly upset and crying — didn’t want him arrested. Officers arrested McDonald, though, finding he was the aggressor and he had caused a “visible injury” to his fiancée, the district attorney’s office said.

That morning, prosecutors said, McDonald’s fiancée sent a text to an unnamed person saying, “Sh— got way outta hand.”

“The incident consisted of a physical struggle between two parties, each party blaming the other, no verifiable eyewitness accounts, and no one left with significant injuries,” the district attorney’s office said.

McDonald’s fiancée refused to cooperate with investigators, and would not allow them take pictures of her injuries for evidence, which made proving whether McDonald used unreasonable force against her difficult, the district attorney’s office said.

In addition, officials said, everyone interviewed by police denied seeing the altercation, except for one of McDonald’s teammates. But prosecutors said the statement from that player, whom they did not identify, “lacks credibility.”

The McDonald case was complicated by the fact that when police responded to the fiancée’s 911 call, Sgt. Pritchard was already there and in uniform. Pritchard, who worked security at Levi’s Stadium in Santa Clara, has not commented.

“The relationship between Sgt. Pritchard and the 49ers, and possible relationships between other San Jose police officers and the 49ers, required a thorough investigation including extensive interviews and search warrants to make sure neither perceived nor actual bias compromised the investigation or in turn our charging decision,” prosecutors said.

The incident raised questions about whether officers who moonlight as security guards have conflicts of interest. The San Jose police internal affairs bureau is investigating why Pritchard was at McDonald’s home, and Police Chief Larry Esquivel has suspended more than a dozen officers from providing security for the Niners.

San Jose police officials would not comment on the McDonald case Monday, but said the agency is continuing to review its policies governing officers who work as security guards on the side.

“All secondary employment with the 49ers organization remains suspended until we have had time to conduct a meaningful review and analysis,” police spokeswoman Sgt. Heather Randol said in a statement.

In the wake of McDonald’s arrest, San Jose police also revealed that they had responded to an earlier incident at the player’s home.

In late May, officials said, officers went to the residence to deal with an altercation in which McDonald and his fiancée had an argument involving a gun. McDonald called police, and, at the time, denied that she ever pointed the firearm at him or fired it. During the investigation into the domestic violence incident, however, McDonald changed his story, saying his fiancée fired the gun into the ground as he drove away, prosecutors said.

McDonald was not suspended by the 49ers after his August arrest and has played all season. The team and the NFL have said they would allow the criminal investigation to play out.

“The issue of domestic violence is important to us, as it is throughout society. We have taken this allegation seriously, just as we have taken the principles of due process seriously,” 49ers officials said in a statement Monday.

“We have said from the beginning that we will consider the information available, allow the facts to lead to our decisions and respect the judicial process. Based on the information available to us and the District Attorney’s decision not to file charges, there will be no change in Ray’s status with the team.”

The NFL has been under intense public scrutiny in recent months over how it deals with players accused of domestic violence. Baltimore Ravens running back Ray Rice was cut by his team and suspended indefinitely by the league after video footage surfaced of him punching his then-fiancée in an Atlantic City hotel elevator, knocking her unconscious.

Before the video became public, Rice was suspended two games, which caused a backlash and prompted NFL Commissioner Roger Goodell to institute harsher penalties for players involved in assault, battery, domestic-violence or sexual-assault incidents.

The Santa Clara County district attorney’s office has been under a spotlight for its decisions on criminal charges involving 49ers players who live in the area. The office has charged players in some cases and cleared them in others.

In August 2013, linebacker Ahmad Brooks was arrested after allegedly hitting then-teammate Lamar Divens three times in the head with a beer bottle and punching him in the face in Brooks’ driveway in San Jose. The district attorney's office decided not to file charges, concluding that the two players had a history of conflict and and that Brooks might have been acting in self-defense.

In October 2013, prosecutors charged linebacker Aldon Smith with illegally possessing three assault weapons that he had allegedly bought over the counter in Arizona, while the team was on a road trip. The weapons were found at Smith's home in the foothills east of San Jose after a June 2012 party during which he fired a handgun into the air and was stabbed, and two other people were shot, authorities said.

A judge sentenced Smith to probation on the gun charges as well as an unrelated charge of drunken driving filed against Smith after he crashed his car. Prosecutors said they thought the sentence was fair.

The NFL suspended Smith for nine games because of the Santa Clara County case and other incidents. He will be eligible to play his first game for the team this season Nov. 16.

In April, prosecutors charged cornerback Chris Culliver with misdemeanor hit and run and felony possession of brass knuckles. That followed a March incident in which Culliver allegedly drove without a license, slammed his Ford Mustang into a bicyclist in San Jose, tried to flee and then used the brass knuckles to threaten a witness who followed him. Culliver has pleaded not guilty.

Hamed Aleaziz and Evan Sernoffsky are San Francisco Chronicle staff writers. E-mail: haleaziz@sfchronicle.com, esernoffsky@sfchronicle.com Twitter: @haleaziz, @EvanSernoffsky