MINNEAPOLIS — When a brain tumor took away Dorothy Holm’s ability to speak, she picked up index cards and began filling them, edge to edge, with seemingly random, indecipherable sequences of letters. Her grandchildren saw her scribbling and thought she was leaving them a code — but it was one the preteens couldn’t crack.

Eighteen years later, the puzzle has been solved after one of Holm’s granddaughters posted images of a card online. In just 13 minutes, a MetaFilter.com user figured out that as Dorothy Holm was dying, she was writing out prayers.

“It was kind of relieving to have an answer, even if we don’t know what every single word says,” Janna Holm, who posted the card, said. “It’s nice to know that they were prayers, and kind of gave some insight into what she was thinking and what she was focused on in her last couple weeks.”

Holm said Wednesday that her grandmother, who lived in Shakopee, was diagnosed with lung cancer that metastasized and formed a brain tumor. She died in 1996 when Janna was 11. In her final weeks, she wrote line after line of capital letters on roughly 20 index cards, sparking her grandkids’ curiosity.

Holm said she, her brother and two cousins — then ranging in age from 8 to 12 — spent a few months trying to figure out what the letters stood for, but failed.

Holm’s father recently found one of the cards, and Holm, who loves puzzles, decided to delve into the project once again. She asked for help Monday on MetaFilter.com, a community blog, thinking her grandmother may have been trying to remember lyrics, and that each letter stood for a word in a song.

“This is a crazy long shot, but I’ve seen Mefites pull off some pretty impressive code-breaking before!” she posted.

In the image she posted, the letters fill the front of the card top to bottom. There is some repetition, strokes that look like backward commas and lines that look like stanza breaks. The back of the card contains fewer lines, marked with the numerals 1 and 2.

In minutes, MetaFilter members were on the case. One user — looking at the back of the card — thought about religion and realized that each letter stood for a word in the Lord’s Prayer.

“AGH, YES! ….. OFWAIHHBTN … Our Father who art in Heaven, hallowed be thy name,” the user wrote.

With that, more MetaFilter members worked on the front of the card. Holm guessed it might be a personal prayer. Using her own deductions and comments from the website, Holm compiled a prayer in which her grandmother was giving thanks, and praying that her loved ones would be safe, happy and healthy.

Holm said she’s not sure why her grandmother used a code, but perhaps, as her memory was fading, she used it as a “cheat sheet” to help recall prayers.

Holm, of Baltimore, Md., said the experience has shown her the power of crowd sourcing (she posted that her dad was amazed at the skills of “the internet people”) and it’s been fascinating to learn more about her grandmother.

And after a couple whirlwind days, Janna Holm says she has all the answers she needs.

“I don’t care if a little bit of it never gets solved,” she said. “It’s OK to have a little bit of mystery.”