Four people are being questioned in connection with Saturday's deadly blast in the western Indian city of Pune, police say.
Police Commissioner Satyapal Singh said one of those injured had died in hospital, raising the death toll to 10.
At least 56 others were wounded in the attack at the German Bakery restaurant, which is popular with tourists.
The bombing was the first major strike of its kind in India since the deadly Mumbai attacks in November 2008.
One of the suspects had been taken in for questioning in Pune and another in the neighbouring industrial township of Pimpri, news agency Press Trust of India (PTI) reported. Television news channels said two others had been detained in Aurangabad, about 200kms (120 miles) from Pune.
Mr Singh told reporters a student, 24, admitted to Inlaks Budhrani hospital after the blast, had died on Monday night.
Forensic reports suggested substances used in the explosion had included RDX, ammonium nitrate and petroleum hydrocarbon, he added.
The explosion tore through the German Bakery restaurant, on North Main Road, at about 1900 local time (1330 GMT), when it was packed with diners.
Reports said an unattended package exploded when a waiter in the restaurant attempted to open it.
The German Bakery is near the Osho Ashram, a mystic centre popular with visitors to Pune.
The Chabad centre, run by the Jewish Orthodox Chabad-Lubavitch movement, whose members were targeted in the 2008 Mumbai attacks, is also in the area.
The Indian home ministry has advised all state governments to be on high alert.
The blast came a day after India and Pakistan agreed to meet for talks in Delhi - their first formal negotiations since the Mumbai attacks of November 2008.
India blamed Lashkar-e-Taiba, a Pakistan-based militant organisation, for the attacks in which more than 170 people, including nine gunmen, died.