Drug overdoses took a deadly toll in Santa Rosa over the weekend. Police are investigating the deaths of four young people, and the hospitalization of two more, to see if they are connected to a man arrested for selling narcotics,

The suspect linked to the overdose deaths of two teenagers in Santa Rosa was in court again Wednesday on drug charges related to two other teen overdoses in which the victims survived.

Their sudden passing has prompted an outpouring of grief and raised urgent concerns about the dangers of fentanyl-laced drugs. As investigators work to piece together what happened, here’s what we know so far.