Foster City police have arrested a suspect in the six-alarm fire that gutted the Spinnaker Cove condominium complex and displaced more than 150 people — and the booking charges reach beyond the blaze itself to accuse the person of obstructing the investigation into how it started.

Investigators traced the Aug. 2 fire to an accidental cause: an unattended gas grill on a first-floor balcony. But an accidental spark rarely ends in a jail cell. What turned this one into an arrest is the second half of the allegation — that the suspect also obstructed and delayed the police and fire investigation. Police have not released the person's name, leaving the most consequential fact about the case unanswered even as the booking is complete.

The San Mateo Consolidated Fire Department determined the blaze was caused by an unattended gas grill on the exterior balcony of a first-floor unit at 815 Sea Spray Lane, according to the Foster City Police Department. The fire spread through the attic and insulation of the 51-unit building and escalated to six alarms, drawing crews from agencies across San Mateo County. Four firefighters were hurt — with injuries ranging from second-degree burns to smoke inhalation — while battling the flames and pulling residents to safety. Officials said seven people trapped on the third floor were rescued as neighbors fled with children and pets.

The building is a total loss. It remains fenced off and red-tagged because officials say it is still at risk of collapse, and residents have not been allowed back inside.

According to Foster City police, the suspect was arrested on suspicion of unlawfully causing a fire resulting in injuries to firefighters, and separately of obstructing and delaying the police and fire investigation. The person was taken into custody without incident and booked into the San Mateo County Jail. That obstruction allegation is the detail that distinguishes this case: a grill left burning is negligence, but interfering with investigators is a deliberate act, and it is the reason the department is describing this as an arrest rather than a cause-and-origin finding.

What police have not said is who the suspect is. The department has not publicly identified the person, released the specific counts filed by the district attorney, or explained what led them to the arrest. Patch reported that authorities did not immediately release details about the charges or what led to the arrest. For the more than 150 people trying to figure out where they will sleep next month, the withheld identity is the difference between knowing whether a neighbor stands accused and being left to guess.

The fallout for residents is immediate and material. "You're lucky to see me not crying. I've been crying since last night," displaced resident Ricky Liboro said after the fire, in remarks reported by KTVU. "We lost everything. We're just trying to figure things out at this moment, trying to process everything." The American Red Cross has been assisting displaced residents with shelter and other services.

The gap between what is known and what is public is the story now. Investigators have a cause. Prosecutors have a person in a jail cell. But the arrest of an unnamed suspect on an obstruction charge raises questions a cause-and-origin report cannot answer: Did the person who left the grill also impede the inquiry, or are those two different people? What, specifically, did investigators say was obstructed? Foster City police have not answered, and until they do, the residents of Spinnaker Cove are left with a destroyed building, a determined cause, and an arrest they cannot fully see.