Dr. Lauren Semanchik, a young veterinarian shot dead at her home after months of harassment by an ex-boyfriend, had sought help from the police as she tried to protect herself.

She reported the threatening behavior to the police in her small town in western New Jersey and to a police department near where she worked, records show. According to her relatives, she installed security cameras at her house and in her car, increasingly fearful that she would be harmed by the man — a lieutenant with the New Jersey State Police who worked in the department’s elite dignitary protection unit.

On Thursday, her family announced a lawsuit against several policing agencies.

“She was failed by every single law enforcement agency that she went to for help,” Jennine Semanchik, the slain woman’s mother, said during a news conference announcing the legal action.

After the trooper, Ricardo J. Santos, mentioned wanting to kill himself, months after they split up, Dr. Semanchik reported her concerns to one of his colleagues at the State Police, her relatives said.

Then, they said, she waited for help that never came.

Dr. Semanchik, 33, and a man she was dating, Tyler Webb, 29, were killed Aug. 1, outside her house in Franklin Township in Hunterdon County. Lieutenant Santos was found dead in a white 2008 Mercedes hours later from a self-inflicted gunshot wound, county prosecutors have said.

The same Mercedes had trailed Dr. Semanchik home from work the night she died, and its occupant was spotted “surreptitiously walking through the wooded area” near her home, according to footage captured by a security camera and described by prosecutors.

Mr. Webb’s body was discovered on a rear porch; Dr. Semanchik died in another location outdoors, according to Allison Semanchik, who lived in a basement apartment at her sister’s home.

“She clearly tried to run,” she said.

On Thursday, lawyers for relatives of Dr. Semanchik and Mr. Webb, a volunteer firefighter who worked as a mechanic, announced that they intended to sue the State Police and the police departments in Franklin and Washington Townships, where Dr. Semanchik had sought help. She had described being harassed and asked for guidance — in person and in a follow-up call — on how to file a restraining order.

“He’s a state trooper, so I’m especially uncomfortable,” she said in a voice mail message left on a recording at the Franklin Township Police Department, which was obtained and shared by the families’ lawyer, David Mazie.

“No one called her back,” Mr. Mazie said.

Hunterdon County prosecutors have already seized control of Franklin’s police department and placed its chief and a sergeant on leave, citing “serious concerns” about the agency’s “operations and effectiveness” in light of the killings. Hunterdon County is also handling the murder investigations.

A captain who is now in charge of Franklin’s police department declined to comment. Officials in Washington Township, in Morris County, could not immediately be reached for comment.

Lieutenant Santos had worked for years in a State Police unit of select troopers assigned to guard prominent New Jersey officials, including the governor, the attorney general and the leaders of the Assembly and Senate.

During Philip D. Murphy’s first term as governor, Lieutenant Santos worked with a unit that guarded Mr. Murphy and his family around the clock — at their home in Middletown, N.J., and at Drumthwacket, the state’s Executive Mansion in Princeton.

The trooper, who was in his 40s, was ambitious, regularly volunteering for extra overtime shifts on weekends and holidays, according to former co-workers and a supervisor. After leaving the governor’s security squad, he was assigned to protect the first assistant attorney general.

Investigators found a note in his home after his body was discovered. Written with what appeared to be three different pens, the note expressed extreme dissatisfaction with the State Police, according to several law enforcement officials with knowledge of the investigation. The lieutenant identified a half-dozen colleagues by name and said he felt bullied, the officials said.

In early spring, Dr. Semanchik had contacted one of Lieutenant Santos’s colleagues to report his erratic behavior and to share that she feared he might be suicidal, her relatives said.

Then, about a month later, on May 19, she reported to the police in Washington Township that her car had been vandalized while she was at work, according to a police report. The investigating officer called Lieutenant Santos, noting in a report that he told the trooper “he should avoid all contact with Lauren as to not escalate the situation any further.”

The lieutenant stated that he understood, the officer wrote.

The next day, Dr. Semanchik went to a police station in Franklin Township to ask for guidance. She was given a phone number to call and left a message on an answering machine later that day.

“I’m looking to file a police report or potentially even a restraining order against my ex-boyfriend,” she can be heard saying on the recording. She added, “I just stopped in the office, but no one was available.”

Relatives said Lieutenant Santos had called and texted Dr. Semanchik after the couple stopped dating in September 2024 until she blocked his phone number. She also suspected that he had placed recording devices in her home and had begun following her, leading her to install cameras in her car, they said.

It is unclear what happened after Dr. Semanchik lodged her concerns with Lieutenant Santos’s colleague. A spokesman refused to address the topic, saying that the State Police “does not comment on pending litigation.”

Mr. Mazie, the lawyer, pointed to a manual of State Police policies and procedures involving domestic violence incidents that he said should have guided all three agencies’ responses.

“Whenever an officer is involved in a domestic violence incident, either as an alleged perpetrator or as a victim, internal affairs must be promptly notified,” the manual states. “Where the officer was the alleged perpetrator, investigating officers must seize their service weapon or any other weapon possessed.”