(CNN) Another transgender person was killed in Dallas, bringing the reported total to three in less than a year, along with a nonfatal stabbing attack, but it isn't the first time this type of violence has shaken the city.

The Dallas Police Department is investigating four attacks on African-American transgender women, all since 2017, police Maj. Vincent Weddington said.

Police and local media reports indicate, however, there have been other killings of transgender women in the city going back to 2015, though at least one yielded an arrest and others are not classified as murder investigations.

Activists and civil rights groups note the pattern of violence is not unique to Dallas, and said the number of homicides might be higher than the official tally because police sometimes misreport victims' genders.

Here's what we know about the victims in Dallas:

Chynal Lindsey

Her body was found in White Rock Lake, a northeast Dallas reservoir, over the weekend, making Lindsey's the most recent case . The Arlington 26-year-old's body showed "obvious signs of homicidal violence," Police Chief Renee Hall said.

The chief promised an aggressive investigation into Lindsey's slaying and urged the community to remain vigilant. The FBI says it stands ready to join the investigation.

Chynal Lindsey's body was found this weekend in White Rock Lake.

"The FBI is committed to investigating all federal crimes and providing assistance to our local partners when asked," the agency's Dallas bureau said in a statement. "If in the course of the local investigation, information comes to light of a potential federal civil rights violation, the FBI is prepared to assist."

As authorities work to determine whether Lindsey's slaying and others constitute hate crimes -- which would likely come at the federal level, because Texas law provides no special protections for transgender residents -- cousin Tamaya Lindsey told CNN affiliate KTVT that only hate could drive such evil.

"If this was a hate crime, shame on you," she said, breaking into tears. "For someone to have that much anger and hatred toward someone to leave them in a lake like trash, it's horrible."

Muhlaysia Booker

Booker was found shot to death May 18 in south Dallas, where she was born and raised. Her death came shortly after she was assaulted by a mob , drawing attention to a pattern of violence against transgender women of color.

In five weeks, the 22-year-old went from a symbol of transgender resistance -- catapulted into the national spotlight after a video showed her fighting back against a mob attack -- to a martyr.

In a press conference last week, Weddington said the department is investigating possible links between Booker's slaying and other acts of violence involving transgender women, including the stabbing of another woman in April.

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However, police say there is no evidence linking the mob assault to her murder.

At Booker's funeral, her mother said Muhlaysia once told her she would do whatever it took to live her truth, even if it cost her life.

"She was willing to die behind it," Stephanie Houston said . "That's why it's well with my soul."

Edward Thomas was arrested in connection with Booker's assault in April, but Weddington said he was not linked to her killing. Thomas' lawyers, Andrew Wilkerson and Michael Campbell Jr., said he had nothing to do with her death and that the alleged assault was not a hate crime.

"We have no doubt that the truth will come to light in this situation after a thorough investigation," the attorneys' statement said

An unidentified 26-year-old victim

A 26-year-old transgender woman was stabbed multiple times April 13, Weddington told reporters

"Fortunately, the victim in this case survived her attack and provided detectives with a description of the suspect," he said. "The detectives are working diligently to determine if there are any connections to the other investigations."

Brittany White

On October 21 of last year, Brittany White was found shot in her vehicle and police have no suspects, Weddington said.

Weddington did not provide extensive details on White's killing, but he said following Booker's death that two of the crimes bear similarities.

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"During the course of these investigations, detectives have learned that besides all victims being transgender females, two of the victims were in the area of Spring Avenue and Lagow Street prior to the offenses occurring," he said. "In addition, it has also been determined that two of the victims got into a vehicle with someone. In another case, the victim allowed someone into their vehicle."

He did not elaborate.

"Everybody needs to be vigilant and pay attention to their surroundings when they're out in public, and use caution when interacting socially," Weddington said.

Nicole Hall

It is not clear whether Hall's death is classified as a homicide, but the uncertainty over what led to her demise rattled the city's LGBTQ community, especially as it came just days after another transgender woman was strangled.

On the evening of May 12, 2018, a kayaker found a body floating in White Rock Creek and called police, who arrived to find a black, transgender woman's body in a black shirt and scrub pants decomposing in the water.

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Police initially identified the victim by her birth name, but local media quickly provided the proper identification: Nicole Hall, 39.

A detective was assigned to the investigation but it was classified it as an unexplained death. Police have said they will provide more information as it becomes available.

At a vigil for Hall, friends described her as a matriarch of the transgender community and said the death of two transgender women in the span of three days had left them panicked, according to KTVT

"I want to say to anyone who didn't know her ... she was worth knowing," best friend and former roommate Mieko Hicks told the Dallas TV station. "She was someone who was charitable, compassionate. She helped anyone she could. She was sweet."

Carla Flores-Pavon

Three days before Hall's body was found, 26-year-old Flores-Pavon was found strangled to death in her Dallas apartment, according to KTVT

Police told the station she was not targeted because she was transgender but was killed during a robbery.

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A Seabrook, Texas, man was arrested during a May 17, 2018, traffic stop after police found items that belonged to Flores-Pavon in his car, KTVT reported. Police said Flores-Pavon had met the 25-year-old man in an online chat room.

He is being held on $500,000 bail, charged with murder.

Another unidentified victim

This was the first of what Weddington says are the four open cases. Details are slim.

In July 2017, the remains of a transgender woman were found in a field, but the cause of death was undetermined and it was classified as an unexplained death, according to police.

Shade Schuler

The 22-year-old Schuler's body was found the morning of July 29, 2015, in a field on the west side of the city, according to police, who said there is minimal information available about the crime.

Authorities initially identified Schuler as a black male and requested the public's help in finding her killer, but four years later, the homicide remains unsolved.