DENTON, Texas — A man convicted of killing his ex-girlfriend at a North Texas business and fleeing to Mexico with their 4-year-old son has been sentenced to 50 years in prison.

A Denton County jury on Monday convicted 27-year-old Ricardo Alfonso Lara-Martinez of murder in the December 2014 death of Maria Isabel Romero Medina. Her beaten and strangled body was discovered at a Denton insurance and tax office where she worked.

Prosecutors believe Lara-Martinez, who was sentenced Tuesday, and the 27-year-old victim argued over custody and his plans to take the boy to Mexico for a week.

Investigators say Lara-Martinez and his son were already in Mexico when the killing was discovered. The boy, now 7 years old, was located in 2016 and returned to relatives in Texas.

Lara-Martinez was extradited last June.