HOUSTON (AP) — Investigators have recovered a weapon that may have been used to kill a 5-year-old Houston boy whose body was allegedly kept in a storage unit before being discovered in an East Texas motel. 

The weapon was being tested to see if it was the one used to kill Samuel Olson, Andrea Beall, a prosecutor with the Harris County District Attorney's Office, told reporters Thursday.

"We're not going to stop until we get justice for little Samuel," said Beall, who declined to say what type of weapon was found or used to kill the boy.

The disclosure came the same day a third person was charged in the case. All three face evidence tampering counts and none have been charged with murder, though prosecutors said earlier this month that they expected to bring additional charges against one of them, Theresa Balboa, who was Samuel's father's girlfriend.

Samuel's cause of death was ruled a homicide, but authorities haven't said how he was killed. 

A Jasper County grand jury indicted 27-year-old Dylan Walker on Thursday. Court records didn't list an attorney who might speak on his behalf. Balboa and her roommate, Benjamin Rivera, were previously charged.

Authorities allege that on June 1, Walker helped Balboa move Samuel's body from a suburban Houston storage unit to a motel in Jasper, about 135 miles (215 kilometers) to the northeast, where it was found inside a plastic tote in a room Walker rented for Balboa.

Police believe Samuel, who would have turned 6 on May 29, died weeks before Balboa reported him missing on May 27, according to an arrest affidavit. His body was kept in a bathtub at Balboa's and Rivera's suburban Houston apartment until they put it in the tote and hid it in a storage unit on May 13, police allege. 

After Walker helped Balboa move the body to Jasper, he called authorities to let them know where it was, police allege. Prosecutors said Balboa was on her way to Louisiana when she was arrested in Jasper. 

Balboa, 29, remains jailed on bonds totaling $600,000. Rivera, 27, and Walker were freed after posting bond. 

"I'm thankful justice is beginning to be served," Sarah Olson, Samuel's mother, said in a statement. 

Samuel's parents had been involved in a bitter custody battle since filing for divorce in January 2020. His mother had primary custody, but she hadn't seen her son since the summer of 2020, according to her attorneys. 

Samuel had been living with Balboa since April 30, which was the last day he was seen at school. Authorities haven't said why Samuel had been staying with Balboa instead of his parents. 

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Follow Juan A. Lozano on Twitter: https://twitter.com/juanlozano70