Cubs first baseman Anthony Rizzo, an alumnus of the South Florida high school where officials say at least 17 people have died in a shooting attack, sent his condolences and encouragement Wednesday on Twitter while sounding a note of alarm.

Rizzo, who in November donated $150,000 to his alma mater, Stoneman Douglas High School, for the installation of lights for baseball and softball fields, said he hoped the people of Parkland, Florida, would come together in “this darkest of times.”

Rizzo, 28, was selected out of Stoneman Douglas by the Red Sox in the sixth round of the 2007 draft.

The Broward County sheriff said a 19-year-old suspect was in custody and that investigators were starting to investigate the attack at the school.

The suspect, a former student, was previously expelled for disciplinary reasons, Sheriff Scott Israel said. Most of the fatalities were inside the building though some were found fatally shot outside.

Information from The Associated Press was used in this report.