More than 400 people have been killed in a string of serial bombings across India since October 2005, with Jaipur the latest city attacked. The BBC's Subir Bhaumik looks at who might be behind the blasts.
When Mohammed Jalaluddin - alias Babu Bhai - was arrested in the northern Indian city of Lucknow last year, he told his interrogators that Jaipur was one of their "prime targets".
India's security forces have not come up with convincing answers
"I remember he clearly mentioned two cities, the holy town of Hardwar on the banks of the Ganges and the city of Jaipur as being on their list of targets and we alerted everybody concerned," a joint director of India's federal Intelligence Bureau (IB), told the BBC.
The official was part of the team who questioned Jalaluddin.
Jalaluddin is accused of being the "Indian operations commander" of the Bangladesh-based militant group, Harkat-ul-Jihad-al-Islami (Huji), at the time of his arrest.
A native of West Bengal, Jalaluddin was trained in Bangladesh and then sent to unleash terror in India in 1999, officials say.
He claimed involvement in the July 2006 serial train bombings in Bombay, in which 187 people were killed.
"He told us that a Huji operative in Bangladesh called Jahangir gave him all the explosives for the Bombay blasts. Jahangir is a Bangladesh national," said the Intelligence Bureau joint director, who did not want to be named.
On the basis of Jalaluddin's confessions, India's Intelligence Bureau did issue advice last year, listing a number of cities like Jaipur that it said were on the "hit list" of the jihadis.
RECENT BOMB ATTACKS
August 2007: Bombs in open-air auditorium and restaurant in Hyderabad kill more than 40
May 2007: Bomb in historic Hyderabad mosque kills 14
February 2007: Twin blasts on train travelling from Delhi to Pakistan kills at least 66 people near Panipat
July 2006: More than 160 killed by seven bombs on train network in Mumbai
March 2006: Bombs at Hindu temple and railway station in Varanasi kill 15
October 2005: Three blasts in Delhi kill 62
Then for a few months nothing happened and the intelligence advisory was forgotten.
"That is how intelligence works in India. A general advisory on the basis of some confession or an agent report is usually forgotten when nothing happens for a while," says Bibhuti Bhusan Nandy, a former deputy chief of India's Research and Analysis Wing (Raw), that is responsible for external intelligence.
"The intelligence agencies rarely chase up leads to get more specific intelligence and when something like Jaipur happens, they refer to their old report to save their jobs."
After Tuesday's serial explosions in Jaipur, India has again blamed "the foreign hand" - perhaps a euphemism for Pakistan.
Indian intelligence officials say the new democratically-elected government in Pakistan has stressed it wants to improve relations with India.
It has even promised to deport Dawood Ibrahim - the mafia don blamed for bombings in Mumbai in 1993 - which they say has not gone down well with Pakistan's Inter Services Intelligence (ISI).
"Dawood is a prize asset for the ISI, so they will do anything to save him. They want to spoil the climate of improving relations. So we first have infiltration attempts in Kashmir and gun battles along the border after a long time, then we have Jaipur.
"This is time-tested ISI tactics," says Maj Gen Gaganjit Singh, a former deputy chief of India's Defence Intelligence Agency (DIA).
Blasts in Delhi in 2005 caused carnage in city markets
Indian officials say that the ISI now operates more through Nepal and Bangladesh, where they have developed a secure network of operatives who liaise with militant groups such as Lashkar-e-Toiba or the Harkat-ul-Jihad-al-Islami.
"A good number of terrorists, reportedly with Pakistani intelligence support, found Bangladesh as a safe haven. The collective strength of terrorist groups like Harkat-ul-Jihad-al-Islami, is now estimated in several thousands. India is their principal target," says a former chief of the Intelligence Bureau, Ajit Doval.
Indian intelligence says in recent months, most major explosions have been traced back to Bangladesh.
"The masterminds were Bangladesh nationals, members of groups like Huji, the explosives were procured in Bangladesh and smuggled across the border and Jaipur may not be an exception to that," says Bibhuti Bhusan Nandy.
"The Huji and the Lashkars have scores of sleeper cells all over India ready to strike on direction from outside."
The government of Bangladesh says it is working to curb the activities of Huji. It banned the group in October 2005 and its leader is currently in prison.
In recent years, Bangladesh has itself been targeted by bombings carried out by Islamic militant groups.
But the real strength of the Islamic jihadi groups responsible for explosions in Indian-administered Kashmir and other Indian states lies not so much in the "foreign hand" but in the proliferation of these "sleeper cells" within India.
Usually a sleeper cell contains no more than three to four militants, armed and trained but asked to lie low until definite orders.
No group has admitted planting the Jaipur bombs
The Intelligence Bureau estimates the number of these jihadi "sleeper cells" as running into a few thousands.
"They have thrived on Muslim alienation in India since the phenomenal rise of the Hindu right in the country in the mid-1980s," says Pradip Bose of the Calcutta-based Center for Study in Social Sciences (CSSS).
He says it all started with the demolition of the Babri Mosque in Ayodhya in December 1992 and has been fuelled by large-scale violence against Muslims, such as in the Gujarat riots in 2002.
"A riot like Gujarat creates a few thousand potential jihadis seeking revenge, so there's no use blaming the foreign hand. We in this country have created this problem," says Mr Bose, a distinguished sociologist.
A US state department report has put India at the top of the list of countries worst afflicted by terrorism.
It says that India had more than 2,300 terrorism-related deaths in 2007 - about 10% of a worldwide figure of 22,000 terrorism-related deaths that year.
That is an astonishing number considering many of those 22,000 worldwide deaths occurred in Iraq and Afghanistan where wars are being fought.
It's not just the Islamic jihadis but also separatists like the United Liberation Front of Assam (Ulfa) and Maoist rebels in India who use serial bombings on a regular basis.
The US report also questioned India's "outdated and out burdened law enforcement and legal systems".
"Until we modernise our intelligence gathering and hold it publicly accountable, we cannot win the fight against terrorism," says Amiyo Samanta, a former Intelligence Bureau joint director and retired chief of police intelligence in West Bengal state.