(Image Credit: Scott Olson/Getty Images)

BILOXI, Miss. - Rick Santorum said today that if a U.S. soldier shot and killed 16 civilians, as U.S. officials have suggested, then the Afghan people deserve an apology.

After an energy conference here, Santorum told reporters that the incident needs to be investigated further, calling it a "horrible situation."

"If it turns out to be the case that this person did a horrible wrong and it was a deliberate act, a deliberate act by an American soldier and that is something we should clearly say was something that we should apologize for," Santorum said. "That it's not a mistake, it wasn't something that was inadvertent. This was something that was deliberately done by an American soldier to innocent civilians. It's something that the proper authorities should apologize for, for not doing their job in making sure that something like this wouldn't happen, something like this should not happen in our military period."

Santorum has repeatedly condemned President Obama for "apologizing" for America, including most recently the apology the president offered Afghans for the accidental burning of Qurans by U.S. soldiers. The burning caused riots in the country.

The former Pennsylvania senator said earlier today that the president's 2014 withdrawal timeline for Afghanistan made a "winnable operation very, very difficult." The timeline was actually set by NATO leaders in November 2010.

The pace of the withdrawal will depend on several factors but Obama spokesman Jay Carney would not comment today on whether Sunday's shooting was among them.

Obama called Afghan President Hamid Karzai Sunday to offer condolences to the Afghan people, according to a statement from the White House. He also pledged to investigate the incident and "hold fully accountable anyone responsible."

On election matters, the Santorum campaign released a delegate memo a day before Mississippi and Alabama vote that basically amounted to a rebuttal of the Romney campaign's argument last week that the nomination was all locked up and that Santorum needed 65 percent of the delegates in each contest going forward. In Biloxi, Miss., Santorum stressed that it will be "difficult" for any of the candidates to get to that 1,144 number.

"I think you've been listening to math class and delegate math class instead of looking at the reality of the situation," Santorum told reporters. "The reality of the situation is that … it's going to be very difficult for anyone to get to the number of delegates that is necessary to win with the majority at the convention. I think that's what the math is pretty much showing."

He admitted that the race for this state and Alabama, which also votes Tuesday, will be "tough." The race is tight  among Santorum, Mitt Romney and Newt Gingrich in both states, according to several polls. The candidate said he's been "playing catch-up" here because the other campaigns have "been running ads longer" and campaigning here more than he has.

Santorum had a significant financial disadvantage over his opponents at the beginning of the primary, especially Romney.  But that is no longer the case.  The campaign raised $9 million to Romney's $11.5 million in February and he has a super PAC working on his behalf as well.

A slimmed-down campaign with less of the trappings of a traditional one, including spending less money on advertising and a smaller team, is a hallmark of their operation. Santorum  told voters here and in Alabama that if they want a "conservative nominee" they should "make it a two-person race," making it clear he thinks if he is the victor in these Southern states, it will edge Newt Gingrich permanently out of the running.

"Clearly, if we are successful here, it can have a very, very positive effect," Santorum said. "People of Mississippi and Alabama want a conservative, for sure. They want to elect a conservative nominee. I think we're going to get one either way. But if they want a conservative nominee for sure, they can do that by lining up behind us and making this race clearly a two-person race outside of the South, which it already is, but it can make it even more demonstrative."

Santorum jabbed the president during his address at the Gulf Coast energy summit,  calling opposition to offshore drilling and increased regulation of oil production here "politicization of science."

This region was devastated financially and environmentally by the 2010 Gulf oil spill. He also called climate change "politicization," and while he believes the "earth does warm, the earth does cool," it's because "it always has, it always will.

"The idea that one particular factor is the driving force behind it that would cause cataclysmic effects is unscientific and therefore we're not going to support any type of dramatic and vague changes to our laws that even those who support those changes will tell you is not going to have any impact on the so-called man made global warming," Santorum said. "So this is simply folly, folly in the sense that putting forth proposals that don't even solve the problems that they say that exist, which is speculative at best."

He said he could point reporters to "a whole host" of sources and scientists to back up his claims.

ABC News' Ann Compton contributed to this report.