HARRISBURG — Senate Democrats said they have hired an outside law firm to investigate a complaint by a woman who alleges that State Sen. Daylin Leach sexually assaulted her nearly three decades ago, when she was a teenager and he was a lawyer defending her mother on an attempted homicide charge.

Senate Democrats said their decision to investigate was triggered when Cara Taylor, an Allentown-area woman, distributed to them this month a private criminal complaint she filled out but has not been formally filed with the Lehigh County district attorney. In the complaint, Taylor alleges that Leach lured her into oral sex in 1991, when she was 17. Taylor said she had spoken with Lehigh County prosecutors about it, but District Attorney Jim Martin said Thursday night that he had not seen a formal complaint.

The Inquirer and Daily News do not identify victims of alleged sexual assault unless they agree to be named, which Taylor did.

Leach, a Democrat who has represented Montgomery County’s 17th Senate District since 2009, has denied the allegations. He did not return phone calls Thursday night seeking comment on the inquiry, first reported by PennLive.

However, in a seven-paragraph statement posted on his Twitter account Thursday, the senator promised to file a defamation lawsuit in Philadelphia Common Pleas Court against “some of the leaders of the effort to defame me.” He did not name them, but referred to “a small group of about 6-8 people” that he said has harassed him. Earlier this month, for instance, protesters burst into a Pennsylvania Medical Cannabis Society dinner in Harrisburg where Leach was the keynote speaker.

“I have spent my career as a lawyer, an activist and a legislator fighting injustice,” he wrote. “This is an injustice.”

He said the situation has been “extremely difficult for me, my family my staff, and my friends.”

In an interview, Senate Minority Leader Jay Costa (D., Allegheny) said he decided to hire the law firm Eckert Seamans to remove any perception that Leach’s colleagues are “directing the outcome of this" investigation.

“If we did it internally, there could be some who would say we manufactured the outcome we desired,” said Costa. “Listen, whatever happens, there will be findings, and they will be reported back to me.”

Costa said Leach has indicated that he will fully cooperate with the investigation. The Democrats say they intend to make the findings public.

Before he joined the Senate, Leach worked as a lawyer, and in the early 1990s represented Taylor’s mother, Kathleen Speth. Speth was charged with attempting to kill her then-husband by attaching a hose onto the exhaust pipe of her car and snaking it into his bedroom while he slept.

In her complaint, Taylor, previously known by her maiden name, Kunz, said that she made a decision to falsely take the blame for her mother’s crime — a move that later led to a perjury conviction.

Before the trial, Leach picked her up at her home and drove her to his apartment “telling me we had to talk about my mother’s case," she said in the complaint.

Taylor wrote that Leach got a himself a drink, “disappeared into a room and then called my name.” When she went into the room, she said, Leach was naked with an erection and asked her to “come help me out,” according to the complaint.

“I did as I was told” and engaged in oral sex with him, she wrote.

Taylor wrote that she decided to come forward with the allegations after the Inquirer and Daily News reported in late 2017 that Leach had engaged in questionable behavior with young female staffers and volunteers, from highly sexualized jokes and comments to touching they thought inappropriate.

At the time, he blamed the accusations on an unnamed political opponent and denied ever inappropriately touching women. He noted that he sometimes does touch people when he is talking to them and that “some people subjectively find such touching unpleasant.”

Taylor wrote that she was renewing her allegations in hope that this type of “behavior can be prevented from happening to someone else.”

This is not the first time these allegations have been leveled against Leach. Taylor’s mother, who was convicted, filed a 1993 complaint to the state disciplinary board that oversees attorney conduct. The board said in a letter that there was not enough independent evidence to verify her complaint.

Her mother also raised the issue again in a petition for post-conviction relief. During a 1999 hearing in the matter, Leach took the stand and denied an inappropriate relationship with Taylor.

He maintained that position in multiple interviews with the Inquirer and Daily News last year.

In the interview Thursday, Costa said that there was no timeline to wrap up the review, and that Leach will remain in his position as the ranking Democrat on the Senate Judiciary Committee and continue to participate in Senate meetings and affairs.