Pamela Butler vanished before Valentine’s Day 2009. (Butler family)

It took eight years for a key witness to come forward and help police arrest a suspect in the disappearance and likely death of Pamela Butler.

The District woman had vanished before Valentine’s Day in 2009, and her boyfriend, Jose Angel Rodriguez-Cruz, was a suspect from the investigation’s earliest hours. He denied to police and the news media any involvement.

But around the eighth anniversary of Butler’s disappearance, confronted by another Valentine’s Day without answers, a veteran D.C. homicide detective assigned to give fresh looks to cases gone cold picked up the file.

The detective, Michael Fulton, found a witness who revealed startling details about the boyfriend. The witness said he had seen Rodriguez-Cruz hold a gun to the head of a previous wife as she begged for her life. And he told detectives that 22 years ago, he had found a letter Rodriguez-Cruz wrote, admitting he was “responsible” for the disappearance of his first wife.

Now Fulton found himself investigating the disappearances of not one woman but two. Neither Butler, a 47-year-old computer analyst for the Environmental Protection Agency, nor the first wife, Marta Rodriguez, a 26-year-old nurse’s aide who went missing in 1989, has been found.

“It was time for the truth to be told,” the witness, who has not been publicly identified, told Fulton. The letter and other evidence were disclosed in court documents made public Monday, three days after police arrested Rodriguez-Cruz, 51.

Police have charged him with first-degree murder in the case of Butler, whom a judge declared dead in 2016. Authorities in Arlington County and in the District have reopened the case involving Rodriguez, who D.C. police said in the affidavit is believed to be dead.

Police described the account of the letter as a key building block in a case based largely on circumstantial evidence, much of it centering on the suspect’s past links to domestic violence and threats involving four women, two of whom are missing.

The witness who found the letter told police that he returned it to Rodriguez-Cruz “and never saw it again.” According to the affidavit, the letter in part said, “I Jose Angel Rodriguez Cruz am responsible for Marta’s disappearance.”

In court Monday, longtime homicide prosecutor Deborah Sines said Rodriguez-Cruz was a jealous lover and had a pattern of abusing women. She said that Butler was about to break up with him and that he killed her because of that. The prosecutor noted that in an unrelated domestic abuse case, Rodriguez-Cruz once told a police officer: “I’d rather see her dead than be with someone else.”

“He has a penchant for violence that is well-documented with several women,” Sines said. “He’s dangerous. He’s unstable, and he’s a danger to the community.”

Rodriguez-Cruz’s attorney, Judith Pipe of the District’s Public Defender Service, said in court that the government could not even prove that Butler was dead and that there was no evidence tying her client to a crime. “There is no blood. No murder weapon or any information that there was even a struggle,” Pipe said.

Several members of Butler’s family attended Monday’s court hearing. Outside, Fulton hugged them. Sines called the detective “relentless” in his pursuit.

The suspect, in interviews with The Washington Post in 2009, blamed emotional problems on his military service in the 1980s, when he said he suffered post-traumatic stress disorder after being ordered to kill civilians fighting in El Salvador. D.C. police interviewed Rodriguez-Cruz extensively in 2009 and reported finding no incriminating evidence inside Butler’s house or in ­searches of the suspect’s residence or vehicles.

Court documents say that after one of those 2009 sessions with police, he started to cry and complained that Butler overpowered him emotionally. He denied killing her but said, according to a 51-page affidavit, “Man, for some reason I can’t get Seneca State Park out of my mind. I keep seeing her in Seneca Park.” Police said they searched the 6,300-acre expanse along the Potomac River in Montgomery County but found nothing.

Rodriguez’s relatives could not be reached Monday. She was last seen walking to a bus stop in front of St. Elizabeths Hospital in Southeast Washington, where she worked as a nurse’s aide. Her family is from Puerto Rico.

Court records from Virginia in 1989 document a tumultuous relationship. Rodriguez-Cruz was stabbed during an argument, and another time, Rodriguez told police that he had slammed her head into a car window.

Court documents allege that Rodriguez-Cruz abducted Rodriguez in March 1989, binding her with rope and duct tape, and driving her to a motel. Rodriguez-Cruz was criminally charged, but the case was dismissed when Rodriguez failed to show up in court.

Police said she was reported missing a week later by a roommate in Arlington. The missing-persons investigation was closed when a woman police believed was Rodriguez turned up in Florida, court papers said, but that person, who was known to Rodriguez-Cruz, was falsely using his wife’s identity.

Other women also described Rodriguez-Cruz’s alleged violent streak. Authorities said in the affidavit that Rodriguez-Cruz’s second wife told them he “routinely physically and verbally assaulted her” with knives and a gun. In 2014, a woman who was Rodriguez-Cruz’s boss in Fairfax County said that his “violent rages” were increasing in frequency and that he had threatened to kill her.

Rodriguez-Cruz grew up in Puerto Rico and New York and joined the Army in 1982 at age 17. Court records citing Army reports note behavioral problems, including “unstable interpersonal relationship and unpredictable behavior.”

Rodriguez-Cruz and Butler met in 2008 on the eHarmony dating site. Butler lived at Fourth and Oglethorpe streets in Brightwood, in a home she meticulously maintained and outfitted with security cameras. She was last seen walking into the house with Rodriguez-Cruz the night of Feb. 12, 2009. She worked from home the following day and communicated with co-workers. Her mother reported her missing after she failed to show up at a Valentine’s Day dinner.

The surveillance cameras Butler had installed showed Rodriguez-Cruz in and out of the house in the days after Feb. 13, several times carrying trash bags and once cleaning supplies. He told police that he was removing personal items after they had broken up. Police also said that parts of the house were in disarray and that Butler’s bedsheets and blanket were missing.

Rodriguez-Cruz told detectives that Butler had ended their relationship either the night of Feb. 12 or Feb. 13. That night, at 8:19 p.m., he was seen on video carrying two flowers in a clear plastic bag into the home.

The following night, Valentine’s Day, police said Rodriguez-Cruz visited an ex-girlfriend. She told authorities he brought a teddy bear for her daughter and two roses for her.

Jennifer Jenkins and Rachel Weiner contributed to this report.