OAKLAND, Calif. - A second construction fire the same night as Oakland's massive one this week didn't do much damage but left behind some telling clues.
The apartment complex at 32nd and Peralta streets has 124 units under construction.
The first 80 units are slated to open for rental in December.
But Tuesday morning, someone breached a chain-link fence, and broke a window to light a fire inside.
On Wednesday, workers at the site were joined by federal agents.
"The place was crawling with ATF so you couldn't help but see and hear them," said aluminum subcontractor Ryan Ellis.
Yellow police tape still marks the spot agents honed in on, and the shattered grass still litters the ground.
Photos of the inside of the building show a bathroom with walls and ceiling scorched black by smoke.
What appears to be a porcelain sink is smashed to the floor.
But the fire did not spread, because the arsonist targeted the portion of the complex that is most complete, with walls and floors finished and fire-resistant.
"The fire restrictions and ratings on these multiple-unit dwellings definitely kept it from burning to the ground," said Ellis.
But while that complex escaped destruction, another was burning to the ground.
A mile away on West Grand Avenue, a town-house complex under construction mysteriously caught fire, and went to five alarms, threatening a neighborhood.
It fits a pattern of arsons at residential projects, although its cause and origin are undetermined.
The failed attempt- about a half hour later- was spotted by a security guard who smelled smoke.
During daylight hours, the four-story complex has two guards on patrol.
After dark there are four, who keep watch until dawn.
"Because it's more dangerous after 9 o'clock," security guard Eezeil Shogaa told KTVU.
The opposite side of the complex has forty more units, framed but not nearly as finished, far more combustible should someone torch them.
Shogaa wonders if the fire-setter might try again.
"Yeah, they might come back," he said, "and they did leave some things here the other day like oil and we gave them to the ATF."
The arsonist fled, apparently startled by an approaching guard, and left behind a gas can, along with a lighter, rag and a hammer.
They have been turned over the ATF for analysis, as a National Response Team processes both scenes, looking for connections.
"For 15 minutes, I was questioned, even was asked if I would take a polygraph test," neighbor Jeffrey Mann told KTVU, describing how agents quizzed residents of Peralta Street who live closest to the break-in and fire.
Mann believes he was of particular interest because he has complained repeatedly about early morning construction work disrupting his sleep and vehicles blocking his driveway.
"I don't want to see fires started. but there's a tremendous amount of construction going on in the Bay Area right now, and it impacts neighborhoods in all kinds of ways," said Mann.
"The agent who talked to me was from Tampa, Florida," Mann continued, "and he said he'd been out here to Oakland five times in the last two years about these arsons so it's obviously it's a serious situation."
Dogtown, on the edge of Emeryville, is a changing neighborhood: dilapidated homes alongside remodels, homeless camps alongside new dwellings.
It signals improvement for some, gentrification for others.
The rents at the unfinished apartment complex will range from just over $2,000 for a studio to almost $4,000 for a three-bedroom.
The most vulnerable section of the complex, still in its early stages, is ringed by a tall fence and topped by razor wire as a deterrent to intruders.