The showdown started with an apparent mistake.

At one minute past 4 p.m. on Tuesday, paramedics were notified about an “unknown medical alarm” at Mr. Conditt’s home in Pflugerville. Two paramedics from the Pflugerville Fire Department responded. A person inside the home — it was unclear whom — answered the door and told the medics no one there had called 911. The paramedics cleared out at 4:11 p.m.

From an incident report released Friday by the Pflugerville Fire Department, it now appears that a request by investigators for paramedics to remain near the house was relayed instead as a call for immediate medical aid to the residence. It is possible that Mr. Conditt himself had come to the door or was home at the time, and began to suspect that the authorities were closing in.

Finding paramedics at his door could have been the reason Mr. Conditt drove to Round Rock and appeared to be taking steps that signaled he knew the police were on his trail.