Isiah Robertson visits with guests during the NFLPA Dallas Healthy Huddle launch with Monarch Dental on August 18, 2014 in Dallas, Texas. Cooper Neill/Getty Images for Smile Brands Group, Inc. MABANK, Texas -- Former NFL star linebacker Isiah Robertson was killed in a car crash late Thursday evening near Mabank, southeast of Dallas, authorities confirmed. School district officials said Robertson was a guest speaker at the Grand Prairie High School football banquet that evening, CBS DFW reports. The Texas Department of Public Safety said it investigated a three-vehicle crash at around 10 p.m. near Mabank that involved the former linebacker. According to authorities, a preliminary investigation showed Robertson, 69, was driving a limousine north on SH-198 at an unsafe speed around a curve when he went off the roadway and into a side skid, where he came to a rest facing west. After coming to a halt, another vehicle traveling north struck Robertson's vehicle, which pushed it into the southbound lane. During that time, his limo struck another vehicle that resulted in the deadly crash. Robertson was a former first-round draft pick and six-time Pro Bowl linebacker in the NFL for the Los Angeles Rams from 1971 to 1978. He also played for the Buffalo Bills towards the end of his career. He was also the executive director of the drug treatment center Isaiah House in Mabank. Grand Prairie Independent School District confirmed to CBS DFW that he was a guest speaker at the Grand Prairie High School football banquet Thursday evening. "This is a tragic situation. Our thoughts and prayers go out to Mr. Robertson and his family. This is one of those situations that affect many, many people. Those thoughts and prayers come from the Grand Prairie High School family as well," the district said. © 2018 CBS Interactive Inc. All Rights Reserved.