Beverly Smith lost her son, Alonzo Smith, in November while he was in the custody of law enforcement. She is photographed Aug. 3 in her Washington home. (Marvin Joseph/The Washington Post)

Federal prosecutors announced Thursday that they will not pursue criminal charges against two security guards involved in a deadly November confrontation with a District man at a Southeast Washington apartment complex.

Alonzo Smith, 27, was stopped by the guards after he was spotted running through the complex, shirtless and shoeless, yelling for help. The U.S. attorney’s office offered condolences to Smith’s family for what it called a “tragic incident” but said there is “insufficient evidence” to prosecute the guards.

Prosecutors said Smith suffered a cardiac incident. He was “under the influence of a significant amount of cocaine and was being restrained” by the guards, prosecutors said, “both of which may have contributed” to his death.

After interviewing more than two dozen witnesses and reviewing medical reports and other records, prosecutors concluded there was not enough evidence to prove that the guards “violated Mr. Smith’s civil rights by using excessive force or that they possessed the requisite criminal intent at the time of the events,” according to a lengthy statement released by the office of U.S. Attorney Channing D. Phillips.

The District’s medical examiner last year ruled Smith’s death a homicide. The examiner found that compressions to the torso contributed to his death, and officials said the injury may have occurred as a guard pressed his knee into Smith’s back.

Alonzo Smith, 27, who died Nov. 1, 2015, after being found handcuffed by special police officers in an apartment building in Southeast Washington. (Family photo)

Standing outside the prosecutor’s office, Smith’s mother told supporters and reporters that she was not satisfied with the explanation.

“They are still not giving me any information, so therefore it’s still a coverup and they are still complicit in my son’s murder,” Beverly Smith said after meeting privately with prosecutors before the official announcement.

The encounter unfolded early Nov. 1, 2015, at the complex on Good Hope Road near Anacostia, where the guards were working as “special police.” Such guards are armed, have limited arrest powers and are licensed by the District. They protect schools, libraries, local and federal government buildings, and apartment complexes.

Smith worked as a teacher’s assistant at Accotink Academy Learning Center, a private school in Springfield, Va., for students with special needs and those with troubled histories. His family previously said that he may have been visiting a woman and that the two may have had a dispute.

Authorities said the incident began when complex residents called 911 to report a man racing through the halls, shouting and banging on doors.

In the detailed account issued Thursday, prosecutors said Smith arrived just before 2:30 a.m. to visit a friend and then abruptly returned to his car about an hour later. Multiple witnesses told investigators that they saw Smith running outside — shirtless and shoeless — and yelling for help. One resident saw him trying to climb a fire escape ladder leading to the roof.

Two residents reported hearing a voice telling Smith to calm down and to come down from the ladder.

According to prosecutors, one guard grabbed Smith in a “bear hug-type move, pivoted, and put Mr. Smith onto the floor” after Smith tried to “jump past the special police officer and/or over the railing.”

No witnesses told investigators that they saw anyone chasing or assaulting Smith. Prosecutors also said there is no evidence that either guard “punched, kicked, or otherwise struck” Smith.

D.C. police officers arrived at the complex just after 4 a.m. The scene was captured on police body-camera footage, which was the first such video released by Mayor Muriel E. Bowser (D).

The officers found Smith lying on his stomach on a staircase landing, conscious and breathing. His hands were cuffed behind his back. One of the guards knelt next to him, kneeling “occasionally on” Smith’s lower back, according to prosecutors. The other held Smith’s head down.

The guards told the officers they believed Smith was high on PCP, and an officer shackled Smith’s ankles “in case of a drug-induced violent outburst,” according to the statement.

About a minute after police arrived, prosecutors said, the officers realized Smith had “stopped moving and making sounds, although he still had a pulse.”

Officers administered CPR before Smith was rushed to United Medical Center, where he died just after 5 a.m.

Prosecutors said Thursday that the toxicology screening showed Smith had “an exceedingly high amount of cocaine in his blood,” which can cause hallucinations and erratic behavior similar to reactions associated with PCP.

According to the autopsy, Smith had no broken bones, no injuries to his vital organs, and no signs of trauma to his spine or neck. The autopsy did show “blunt force injuries” — described as abrasions, contusions and hemorrhages — on Smith’s head, neck and torso.

Although the medical examiner ruled Smith’s death a homicide, prosecutors said such a determination is “insufficient, in and of itself” to prove that a person is criminally responsible for the death.

To prove that any officer violated local laws or federal criminal civil rights laws, prosecutors must be able to show that officers “willfully used more force than was reasonably necessary,” a bar the U.S. attorney’s office described Thursday as a “heavy burden.”

Defense attorney Justin Dillon, a former homicide prosecutor, said the large amount of cocaine probably contributed to the decision not to charge the guards.

“The government would still have to prove that they were grossly negligent, and you can’t assume that simply because someone died during an arrest — especially when they had acute cocaine toxicity that may have required more force than usual for the arrest.”

Defense attorneys Danny Onorato and Steven McCool, who represent the guards, declined to comment on the case.

In the year since Smith’s death, his mother has repeatedly sought more information, including the names of the guards, which officials have not made public. She also has taken on a public role as an advocate, speaking out against police brutality and gun violence.

While Beverly Smith met with prosecutors Thursday, about two dozen protesters stood outside the Judiciary Square office chanting, “Justice for Zo,” a reference to her son’s nickname. Representatives from various organizations, including Black Lives Matter, called for an end to police violence and what they described as systemic racism.