The notorious "splash-and-grab" robbers - a group of up to three men who throw hot beverages into the faces of cashiers and clerks at convenience stores before looting the cash drawers - have the full attention of the Philadelphia Police Major Crimes Unit.
"It's a serious concern to law enforcement because of the nastiness of these crimes," said Capt. John Gallagher, head of the unit. "On one of the jobs, you actually had bleach thrown in the face of one of the clerks.
"Now, obviously, that could blind somebody or cause ocular damage. We are also concerned about scalds on the clerks' faces, permanent burns."
There's also worry that the robbers might be armed with more than a hot beverage, he said. They could be carrying knives or guns, and if the robbery doesn't go as planned, they might resort to other weapons.
One of the robbers may have attempted to disguise himself by wearing cat's-eye contact lenses in a robbery in Magnolia, N.J., Wednesday, but that tactic may backfire on him, Gallagher said.
"If that was used to disguise one of the offenders, it actually drew attention to the offenders," Gallagher said. "Because that description has been used repeatedly on some of the anonymous calls we received about that particular robbery.
"So it may have had a reverse effect on the offender if he wanted to disguise himself from the people he was robbing."
Police in the city, suburbs and South Jersey are investigating a total of 19 similar robberies since Feb. 7, the most recent in Magnolia.
Of the 19, three occurred in the city. On Feb. 10, the robbers struck the 7-Eleven on Harbison Avenue in the Northeast. The bandits then struck twice on the 13th, hitting the 7-Eleven on Wyoming Avenue and the Wawa on S. Columbus Boulevard.
Gallagher said his unit is working in conjunction with authorities in the other jurisdictions.
He said cops strongly suspect the offenders are feeding serious drug addictions.
But he is confident they will be caught soon.
Authorities are preparing composite sketches of the thieves from surveillance tapes of the robberies, and the Wawa and 7-Eleven companies, the major victims of the attacks, have chipped in $5,000 apiece for rewards.
"We are pursuing every lead, and we are very confident that we can catch whoever is doing this," Gallagher said.
Wawa officials say security has been stepped up at its stores, and workers have been taught new procedures for dealing with the criminals.
The offenders have been described as men in their early 20s who have thin to medium builds and who were wearing dark clothes.
The method is similar in each case. The thieves pick up hot liquids - coffee or hot chocolate - and wait for an opportunity to approach the cashier. They then hurl the liquid in the cashier's face, scoop up the money and run.
Except for one convenience store, a 7-Eleven in Yeadon, which was hit twice by the robbers, all the stores have been hit only once.