PARIS, Dec. 13 (Xinhua) -- A fifth person was arrested and placed in police custody on Thursday in connection with the gunman who killed three people and wounded many others near the Christmas market in Strasbourg, France,the newspaper Le Figaro reported.

The person was from the circle of Cherif Chekatt, the main suspect in the attack.

Chekatt's mother, father and two brothers are being held in custody for hearing since Tuesday night.

Earlier in the day, investigators questioned the suspected shooter's two sisters and raided a house of one of them in Paris, according to the report, citing a source close to the inquiry.

Chekatt, a 29-year-old Strasbourg native, was armed with a gun and a knife when he opened fire several times on Tuesday and stabbed people near Place Kleber and the Grand'Rue, one of the city's main shopping streets where the Christmas market is held every year.

Three people were killed and 13 were wounded. Five remain in critical condition.

Chekatt exchanged fire with the anti-terrorism Sentinelle force that wounded him before he fled in a taxi. He fought a second time with police in the Neuhof district, according to a Paris prosecutor.

Police launched, earlier on Thursday, an operation in Strasbourg's Neudorf district where he had been last seen after getting out of a taxi that he hailed after the Christmas market attack.

Television pictures showed police cordoning off the Neudorf neighborhood and police vehicles blocking access. Heavily armed officers from anti-terrorist units were deployed for raids linked to the investigation into the assault.

Interior Minister Christophe Castaner told the French Senate that the police operation aimed at "eliminating any doubts as there have been several (such operations) since 36 hours."

The gunman has a criminal record and was known to intelligence services as "at risk for radicalization". He had been convicted 27 times in France, Germany and Switzerland for common law offenses, including armed robberies.

He was also on police watch list for radicalization and was listed as a potential security threat.

A total of 720 police officers, supported by two helicopters, had been involved in a huge manhunt for the attacker.

Asked if police had been instructed to catch the fugitive dead or alive, government spokesperson Benjamin Griveaux had told CNews television that "It doesn't matter. The best thing would be to find him as quickly as possible."

France raised its security threat level to highest, strengthening controls along its border with Germany, where agents from both countries stepped up checks of motorists' identity and vehicles crossing the Rhine river.

No group has claimed responsibility for the attack.