Police initially indicated that Rwsereka looked as if he was fleeing to Burundi, as was reported in the New Times.
Democratic Green party Chairman Frank Habineza refuted this theory.
"That is not true, because his passport was found at his house. I personally saw his passport," he told RFI.
The 61-year-old Rwsereka, who was a founding member of the party, "had no enemies," says Habineza.
There are no suspects, nor apparent motives for the crime. Habineza said that Rwsereka had been threatened, however.
But Philippe Reyntjens, Great Lakes expert at the University of Antwerp says that this murder reminds him of yet another disappearance in Rwanda's recent past.
"Although of course we don't know who did it, the Rwandan regime - and I'm referring to the regime rather than the government - would be a prime suspect. Because again, the regime has done this in the past," Reyntjens says.
"The discovery reminded me of an incident seven years ago in 2003 when another opposition figure, Augustin Cyiza, disappeared. His car was found close to the Ugandan border and the Rwandan government then claimed that he had fled into Uganda and from there on into the Congo. It was fairly clear that he disappeared - in other words, he was killed by the government. And this is exactly the same story."
Reyntjens says that the English-language New Times is really the voice of Kagame, although it claims to be an independent paper.
In the New Times, "the police spokesman stated that there was suspicion that the vice-president of the Democratic Green party had actually attempted to flee into Burundi. And his car was found close to the Burundian border. So it seems very much like what we've seen with that previous incident," he says.
The international community - the United States and the United Kingdom in particular - has defended the current Rwandan government wholeheartedly, says Reyntjens. These two countries are currently watching developments.
"It would be such a risky thing to kill the VP of an opposition party, which, technically speaking, was not really necessary. He wasn't that much of a threat. Had the regime done it and this came out, it would become increasingly difficult for these sponsors [the US and UK] to further offer cover to the regime as it has done in the past," he says.
Only a few weeks ago, international outcry against the murder of Democratic Republic of Congo human rights activist Floribert Chibeya prompted an international independent inquiry.
"If the international community were to take this seriously, then it should act just as it has done for the killing of human rights activist Chibeya in the DRC a couple of weeks ago by requesting for an independent international inquiry and not leaving it to those who might be the perpetrators of the crime," says Reyntjens.
The party has yet to be registered, and is not fielding any candidates in the elections next month.
- Andre Kagwa Rwisereka, deputy vice president of the Rwandan Democratic Green party, was found dead on July 14, nearly decapitated
- Jwani Mwaikusa, defence attorney for Rwanda genocide defendant Yussuf Munyakazi, was shot dead in Tanzania on July 13, 2010
- Jean Leonard Rugambage, deputy editor of Rwanda's Umuvugizi newspaper, was shot dead on June 24, 2010 in Kigali
- Bernard Ntaganda, opposition presidential hopeful was taken in for questioning on June 24, 2010 and is still in detention
- Theogene Muhayeyezu, opposition leader Victoire Ingabire's Rwandan lawyer, was detained on June 24, 2010. He is still in detention
- Hundreds of opposition party members were arrested on June 24, 2010
- Faustin Nyamwasa, dissident Rwandan general, was shot and wounded outside his Johannesburg home on June 19, 2010
- Peter Erlinder, a US lawyer who went to Rwanda to defend presidential candidate hopeful Victoire Ingabire, was detained on May 28, 2010 and released June 18, 2010