Updated at 5:50 p.m. Includes new details in the police investigation.

PLANO — A 45-year-old man is at the center of a "very large and complex investigation" involving attacks on the elderly in North Texas after police linked him to the smothering of a Dallas woman and the attempted smothering of women in Frisco and Plano.

Billy Kipkorir Chemirmir, 45, who police say has a background as a health care worker, is being held in the Dallas County jail on charges of capital murder in Dallas and attempted capital murder in Frisco. His bail is set at $1 million.

He has not yet been charged in the Plano case.

The Dallas man is accused of attacking elderly women, using a pillow to try to smother them and then stealing jewelry and other items from their homes. At retirement facilities in Dallas and Frisco, he pretended to be a maintenance worker to try to get in the door, police say.

Billy Kipkorir Chemirmir

Plano police were investigating an attack on a 91-year-old woman on Monday at an apartment complex for seniors and found evidence linking Chemirmir to Tuesday's death in Dallas of Lu Thi Harris, 81. He was taken into custody late Tuesday.

Authorities suspect there may be other cases in Dallas, Plano, Frisco, Richardson and possibly elsewhere.

Plano Police Chief Gregory W. Rushin said Friday during a news conference that authorities are "in the very early stages of a very large and complex investigation."

"Chemirmir uses health care experience to his advantage targeting and exploiting seniors, some of the most vulnerable people in our community," Rushin said. "This is terribly disturbing."

Authorities say they will be reviewing hundreds of unattended deaths of elderly women, as well as deaths previously ruled as occurring from natural causes, to determine whether there is a link to Chemirmir.

"We're not going to leave any stone left unturned," said David Pughes, executive first assistant chief for the Dallas police. "Right now we do have the one confirmed Dallas offense. ... We're worried we could have more."

Chemirmir has lived in Dallas since at least December 2010, when he was arrested on a charge of drunken driving. That arrest was followed by a string of other misdemeanor crimes that resulted in two convictions for drunken driving and one each for assault family violence, criminal trespass and providing a false identity. In June 2016, he was sentenced to 70 days in the county jail.

Chemirmir declined to comment from jail on Friday.

'About to die'

In the Frisco case, a 93-year-old woman said a well-dressed man knocked on the door of her apartment at Parkview Elderly Assisted Living at about 2 p.m. Oct. 29. He said he was a maintenance worker and asked if she needed anything done, according to a probable cause affidavit.

When she declined, the man forced his way inside and knocked the woman from her walker to the floor. He grabbed a pillow from the couch and attempted to smother her, police say.

The woman told police "she began to pray, believing she was about to die."

The man stole a wooden jewelry box with various pieces inside and left after a few minutes, police say. The woman used her emergency alert button to summon help.

Police found blood believed to belong to the suspect on the pillow used on the woman and sent it for DNA testing.

Frisco Police Chief John Bruce said Friday that the woman didn't have enough of a description for detectives to be able to identify a suspect.

It was only after Plano police alerted Frisco this week to similar offenses in their city that Frisco detectives were able to identify Chemirmir as a suspect in the October attack.

Phone records show Chemirmir's cellphone connected with a cell tower within 0.564 miles of the Frisco woman's apartment at 12:14 p.m. on the day of the attack, according to the probable cause affidavit.

'Don't fight me'

According to probable cause affidavits, a man forced his way into the elderly woman's Plano apartment Monday and told her, "Go to the bed. Don't fight me."

When the woman laid down, the man put a pillow over her face, and she lost consciousness. A friend later found her and called 911. A crew from Plano Fire-Rescue revived her. The woman told police the man stole some jewelry.

Plano police spokesman David Tilley said they believe Chemirmir is responsible for the attack on the 91-year-old woman, but he has not been charged in that case.

As detectives looked into her attack, they discovered several deaths of elderly women at the same apartment complex over several months. The question is whether any of those deaths are linked to Chemirmir, Tilley said.

Rushin said the deaths were initially classified as natural because the women were elderly, they had health issues, and they lived by themselves. "It would be very easy to disguise a crime in that type of activity," he said.

The break in the case came late Monday when Plano police found a March 15 complaint involving a suspicious vehicle at that woman's apartment complex. They traced the license plate from that report to a vehicle driven by Chemirmir.

On Tuesday, Plano police began surveillance at Chemirmir's address. When he arrived at his apartment complex in the 4500 block of Pear Ridge Drive at about 6 p.m., police saw him toss a jewelry box into a trash bin.

Plano police arrested him on an outstanding misdemeanor warrant.

Officers who checked the trash bin found a large jewelry box containing jewelry and a piece of paper with a name that they linked to Lu Thi Harris in Dallas. Plano police requested Dallas police to check on her.

When no one answered the door to her home in the 6600 block of Warm Breeze Lane, police forced their way inside. They found Harris dead in her bedroom, an affidavit stated.

Harris had what's believed to be lipstick smeared on her mouth. A pillow on the bed also had lipstick smears, indicating she may have been suffocated, an affidavit stated.

Public's help needed

Police want anyone with information about Chemirmir, his activities or other possible attacks to call a 24-hour tip line at 972-941-5785.

Right now, there is no evidence anyone else is involved in what Rushin described as "horrific crimes."

"We're going to make every attempt to identify all the victims in the communities across the metroplex and fully investigate this case and provide justice for the victims and for their families," he said.