But the wanted man – Abd al-Karim al-Majjati - was not among those who were the subject of an international arrest warrant, as sources close to the investigation said and Reuters reported earlier on Wednesday.
Instead the Spanish judge investigating the Madrid bombings, Juan del Olmo, issued six other arrest warrants for five Moroccans and one Tunisian.
Sources close to the investigation held firm that al-Majjati was perceived to be the organiser of the Madrid attacks that killed 191 people on 11 March - and said del Olmo could still issue a warrant for him in the future.
Majjati, 36, is wanted in the United States, Morocco and Saudi Arabia. Moroccan investigators describe him as a "warrior" who fought in Bosnia and Afghanistan and who was last seen in Morocco shortly before 11 September 2001.
The Madrid bombings of four commuter trains was the first attack in the West linked to Usama bin Ladin's al-Qaida network since the 11 September strikes on New York and Washington.
The attack was timed three days before Spain's general election and played a role in helping the opposition Socialists to a surprise victory that will remove a strongly pro-American party from power.
The Interior Ministry sent pictures of the six new suspects to the media in the hope that people might recognise them.
On Tuesday, Interior Minister Angel Acebes identified the Moroccan Islamic Combatant Group as the prime suspect in the Madrid blasts.
Nearly two hundred people were
killed in the Madrid blasts
Some news reports have identified al-Majjati as the head of that shadowy group, also suspected of being connected to the Dar al-Baida (Casablanca) attacks of last May, in which 12 bombers and 33 others were killed.
Al-Majjati is also wanted by Saudi authorities in connection with attacks on housing compounds in Riyadh last year.
Spanish investigators have pursued a Moroccan connection and suspected links to the Casablanca attacks almost from the start.
A purported spokesman for al-Qaida claimed responsibility for the Madrid attacks in a videotape that called the attacks revenge for Spanish support of US-led wars in Iraq and Afghanistan. He spoke with a Moroccan accent.
Judge del Olmo on Wednesday freed a Moroccan who had been arrested on Friday. The judge, after interrogating the man, determined there was not enough evidence to send him back to prison, reducing the number of detained suspects to 19.
The judge delayed taking a decision on the other suspect who testified on Wednesday. That suspect, one of the two Spanish-born detainees, can be held until Friday before he must either be formally accused or set free.
Police arrested two other suspects on Wednesday, including one who was picked up for the second time. The 28-year-old Moroccan had been freed by the judge on Tuesday, but a court source said new evidence surfaced.