SAN RAMON — They held hands and kissed as they traversed a local Target, ordered a couple drinks at the Starbucks counter, then left the area in a blue BMW X3 almost as quickly as they’d arrived, authorities say.

To anyone who saw them on the afternoon of July 19, Diego Ananias Arellano Díaz and his 24-year-old girlfriend would have easily blended in with the crowd of shoppers. But during the 12-minute visit, Arellano Díaz allegedly made a fateful decision: He’d be back with two cohorts, equipped with an improvised gas bomb and they were going to blow the front off that store.

At around 2 a.m. on July 20, that’s exactly what happened. Three men — donning masks, a skeleton costume, and blue coveralls — exited the same BMW that was seen there hours earlier, with a getaway driver staying be

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