Castillo became a U.S. citizen in September and sent out a tweet blasting Donald Trump. Here's a photo of her at the naturalization ceremony which she posted on her Twitter feed.

For months there have been rumors she was dating Sean Penn, which she denied. Here's a photo of them she posted on her Instagram account. It seems to me they were just palling up for the El Chapo interview.

According to the New York Times,

The interview with Rolling Stone, probably the first drug trafficker granted in decades, took place at various meetings. It began at the beginning of October, with a trip in the middle of the jungle until you reach the top of a mountain. Surrounded by a hundred of his men and dressed in a silk shirt and black trousers, Guzman met with Penn and Kate del Castillo, a Mexican actress who plays a drug dealer in a soap opera.

The Times reports El Chapo told Penn new details of his July, 2015 prison escape:

The engineers who built it describes Penn, were sent to Germany for training. Motorcycle that moved through a rail system that used the hood to escape was specially modified to operate in an underground environment with little oxygen.

Even when the Mexican troops attacked the place where he took refuge days after their first meeting, forcing him to a flight complicated, Guzman decided to go ahead with the interview with the two actors, via the messaging system of Blackberry and a video sent to Penn and the Castle.

The Times reports Penn said the cartel was informed in advance of surveillance drones:

[T]he Sinaloa cartel was informed when the Mexican army made rounds with surveillance aircraft from large heights which could detect their movements.

Why did El Chapo choose Kate del Castillo?

Reportedly, because of her 2012 tweet to El Chapo. The tweet said:

Today I believe more in the 'Chapo' Guzman on governments to hide me even painful truths, who hide the cure for cancer, AIDS, etc. for their own benefit and wealth ".

She also released a long letter about her beliefs, that included a paragraph addressed to him. You can read the full text here. Essentially, she asked El Chapo to use his huge power for good and said he would be a hero if he helped cure diseases, helped street children, "dealt with corrupt politicians", and trafficked with love. "Life is a business, the only thing that changes is the goods."

She took a lot of flak in Mexico for her tweet and letter, particularly after his escape. She hasn't apologized, and has said it's what she believed at the time. As to his escape, she refused to comment, saying only "its crazy."

Apparently, either that was enough for El Chapo, or maybe he watched her on TV and developed a crush on her. (Penn seems to intimate infatuation may have been the cause.) Whatever moved him, he had his lawyer contact her.

According to the New York Times article:

Castillo, who was contacted through his lawyer after she wrote him a message on Twitter, was the only person he trusted to make efforts for the film, according to the article. Penn learned of the connection of Castillo with El Chapo through an acquaintance in common, and asked if the drug trafficker would agree to an interview.

Penn also described the security precautions taken with phones:

It has that you used mobile phones from low cost, one for each contact, which must destroy, burn or change your encryption, which used Blackphones (a maximum security smartphone), anonymous email accounts where exchanged messages in the Outbox drafts.

Despite this, he wrote: "Don't have the slightest doubt that the DEA and the Mexican Government are monitoring our movements".

From the Rolling Stone article, Penn writes:

The trust that El Chapo had extended to us was not to be f*cked with.

He also points out that El Chapo has a reputation for avoiding violence unless necessary.

I took some comfort in a unique aspect of El Chapo's reputation among the heads of drug cartels in Mexico: that, unlike many of his counterparts who engage in gratuitous kidnapping and murder, El Chapo is a businessman first, and only resorts to violence when he deems it advantageous to himself or his business interests.

As to what prompted him to want to do the interview:

As an American citizen, I'm drawn to explore what may be inconsistent with the portrayals our government and media brand upon their declared enemies.

And, of course, the fact that the war on drugs is a failure:

As much as anything, it's a question of relative morality. What of the tens of thousands of sick and suffering chemically addicted Americans, barbarically imprisoned for the crime of their illness? Locked down in facilities where unspeakable acts of dehumanization and violence are inescapable, and murder a looming threat. Are we saying that what's systemic in our culture, and out of our direct hands and view, shares no moral equivalency to those abominations that may rival narco assassinations in Juarez? Or, is that a distinction for the passive self-righteous?

...Perhaps in the tunnel vision of our puritanical and prosecutorial culture that has designed the War on Drugs, we have similarly lost sight of practice, and given over our souls to theory. At an American taxpayer cost of $25 billion per year, this war's policies have significantly served to kill our children, drain our economies, overwhelm our cops and courts, pick our pockets, crowd our prisons and punch the clock. Another day's fight is lost. And lost with it, any possible vision of reform, or recognition of the proven benefits in so many other countries achieved through the regulated legalization of recreational drugs.

I have nothing but huge praise for Sean Penn and Kate Castillo. I appreciate them doing the interview and taking the huge risks associated with it. And sharing their beliefs about the war on drugs, which just so happen to so closely mirror mine.