New details in arrest of man accused of killing Dallas ISD teacher's assistant

MESQUITE, Texas - New details have been released about how police tracked down the suspect arrested this week for the murder of a Dallas ISD teaching assistant.

Court documents reveal the evidence, including phone records, that led them to the man they say killed Jennifer Mendez.

Police said the two knew each other, but the motive is still unclear.

Mesquite police said this investigation is taking months as they try to piece all the evidence together, including the communication the two had before 24-year-old Mendez went missing. 

The suspect, 34-year-old Sixto Banegas-Matute, has now been transferred from Mesquite to the Dallas County Jail. 

FOX 4 asked Mesquite police if there will be any additional arrests, and they said right now that’s still part of the investigation. 

Mendez was last seen pumping gas and grabbing a drink at a Dallas QuikTrip on September 27.

Police revealed the Dallas ISD teacher’s assistant left the gas station at Highway 175 and Belt Line Road and met up with Banegas-Matute.

Less than two hours later, Mendez’s phone was last pinged near a wooded area off Interstate 20 in Mesquite city limits, the site where Mendez’s remains were found scattered.

According to an arrest warrant affidavit FOX 4 obtained Friday, phone records show Mendez was texting Banegas-Matute as she left the gas station at 8:40 p.m. on the night she disappeared.

License plate recognition units scanned her 2015 Buick as she drove a few miles north on Lawson Road, stopping just before the Mesquite wastewater plant.

At the same time, Banegas-Matute’s phone showed to be in the same area. 

Mendez’s family found her abandoned Buick parked on the shoulder of Lawson Road the day after she didn’t come home. 

According to the arrest warrant affidavit, phone records then tracked both of their phones west on Interstate 20. 

The two stopped about a mile away at a break in a wooded area. 

Mendez’s remains were found tucked behind the trees two weeks after she was reported missing. 

Banegas-Matute’s phone went on to his listed address at an apartment complex in Balch Springs. 

Police believe Banegas-Matute shot and killed Mendez. 

Investigators located bullet fragments in the hair recovered from the scene. 

Mesquite police are not answering any questions regarding a motive and the relationship between Mendez and Banegas-Matute, only saying the two began texting about a month before Mendez vanished. 

Police haven’t released if the murder weapon was located either. 

More than three months later, Banegas-Matute now sits in the Dallas County Jail charged with murder. 

According to public records, Banegas-Matute does not have a criminal history. 

Mesquite police said they are still investigating threatening text messages sent to Mendez’s family and friends after she went missing. 

One read: "Jennifer dead. You are next. You better text me back."

Investigators wouldn’t confirm if these texts came from Banegas-Matute.

However, police said more arrests are possible. 

Mendez's family said they were told by police to not speak on the arrest in an effort to not jeopardize the investigation. 

They said they do not recognize Banegas-Matute.

The family also told investigators Mendez had a boyfriend for the last year. 

Police checked the boyfriend’s phone records and he was confirmed to be at home the night Mendez disappeared.