A man arrested last week in connection with a robbery of a taxi driver in Northeast Washington was freed without being charged, and now police say they are looking for him again in a similar case.

Why the U.S. Attorney’s Office declined to prosecute Miguel Demonis, 19, of Southeast, after Friday’s arrest is unclear. Officials would not say if prosecutors thought that the police case was insufficient to support charges, and a spokesman declined comment on that subject.

The arrest at first appeared to be a break in a spate of attacks on taxi drivers along the Rhode Island Avenue corridor. Now District police and cab operators are back on alert.

“It’s a little frustrating, and a little scary,” said Larry Frankel, head of one of two D.C. cab associations.

Word of the attacks and the arrest spread quickly through the taxi fraternity, according to Frankel. Before last weekend, he said, drivers working in the neighborhood “looked over their shoulders and looked through their windshields at everybody just a bit more closely. ”

After learning the suspect arrested had not been charged, Frankel said, “Maybe I won’t go out tonight.”

Two law enforcement officials said that charges weren’t filed against Demonis in order to give detectives time to try to build a broader case tying in other robberies that took place in the Edgewood neighborhood last week. Those officials said that after prosecutors did not sign off on criminal charges, authorities had to release Demonis — after which police obtained an arrest warrant charging him in a different cab robbery last week.

Demonis was being sought as of late Tuesday afternoon, according to police. He is due in D.C. Superior Court on Wednesday to face sentencing in a misdemeanor pellet-gun case stemming from an arrest in January .

Demonis’s attorney, Bryan Bookhard, declined comment. A D.C. police spokeswoman referred questions to the U.S. Attorney’s Office.

Demonis’s arrest early Friday came shortly after D.C. police announced that they believed a spate of robberies and attempted robberies of taxi drivers by passengers in the Edgewood neighborhood were linked. Authorities hailed the quick action of officers to track down Demonis and an alleged 15-year-old accomplice minutes after the latest holdup.

Police said that after a robbery at about 11:15 p.m. Thursday, extra officers had been deployed to the area and one of them recognized a man fitting the description in the incident. Officers chased Demonis and the teenager, catching them as they tried to hide in a stairwell.

Police issued a news release Friday evening naming Demonis as having been arrested and charged with robbery. The statement said that police were “currently investigating whether these suspects are involved in other crimes.”

The status of the case against the juvenile could not be determined. In the Demonis case, the U.S. Attorney’s Office declined to pursue the charges against him.

U.S. Attorney’s Office spokesman Bill Miller said, “Regarding the questions about the taxicab robberies, the investigation is continuing.”

Demonis is scheduled to appear in D.C. Superior Court on Wednesday for sentencing on a single misdemeanor count of possessing a pellet gun in connection with the January incident.

In that incident, according to court documents, off-duty D.C. police officers at Union Station spotted a possible suspect wanted in an earlier robbery of a taxi driver. Details of that robbery were not immediately available.

The charging papers say that a uniformed officer said he saw Demonis sitting on a bench near the station’s First Street entrance. The court documents state that Demonis and a friend pulled their jackets over their faces as the officer approached, and that Demonis shouted, “Why are you harassing me?”

Demonis jumped up and the officer handcuffed him, the court documents state. The officer said he found a black BB gun, resembling a handgun, under the coat.

Demonis had been freed pending sentencing for that offense.