According to an arrest affidavit, Tellgren and Garza can both be seen on surveillance video getting into a small, dark-colored pick-up truck and leaving the Market Street grocery in Coppell just before 9 a.m. on April 16.
Tellgren had earlier told police he had left Garza at the grocery at 10 a.m. and was unsure of her whereabouts.
Investigators searched the man's vehicle and found the missing woman's purse and large sections of the seat cut out of the vehicle. Officers also found what they believed to be blood in several areas of the truck.
Officials seized the vehicle and took Tellgren into custody.
During an interview later that evening, Garza's watch and two rings were found in Tellgren's pocket. His shirt also appeared to have been stained with blood, police said.
The next day, officers found a black trash bag containing pieces of foam, fabric and a seat belt, along with a denim jacket believed to be Garza's, in a trash bin a mile from Tellgren's home. Officials said all of the items found were believed to be stained with blood.
Since her disappearance, no activity has been observed on Garza's phone or bank accounts and she has not contacted any member of her family, police said. Based on those facts, it is believed the woman is deceased, police said.
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Tellgren has been charged with capital murder and is currently being held on $1 million bond.