Four pad crystals

[Emil]

I'm planning to use a four pad quartz crystal. The datasheet shows pad 1 and 3 to be connected to the crystal. Pad 2 and 4 are not shown to be connected to anything, but it doesn't explicitly say NC either.

What should I do with pad 2 and 4?
1. Leave unconnected.
2. Connect to gnd.
3. Connect 1-4 and 2-3 together (saves space by not needing to route a trace around the pad)

The part is ABM10-167-12.000MHz-T3, datasheet: http://www.mouser.com/ds/2/3/ABM10-167-12.000MHz-962396.pdf

[Rerouter]

In general i connect them to the same ground as the crystal capacitors, and have that ground trace run right back to the oscillator ground pin before it meets the ground plane.

[ataradov]

I've seen justifications for both 1 and 2. But don't do 3, for sure, since in some cases top metal can is connected to one of those unconnected pins, and you will short your crystal.

[wraper]

I've seen justifications for both 1 and 2. But don't do 3, for sure, since in some cases top metal can is connected to one of those unconnected pins, and you will short your crystal.

Actually not some cases but everything I've seen has those pads connected to the metal cover and internal metallization. It's strange that datasheet does not say anything about those pads.
First random datasheet which I found for similar crystal http://www.ndk.com/images/products/catalog/c_NX2520SA-STD-CSW-4_e.pdf (says should be connected to GND)